Table of contents :

B-cell leukemias/lymphomas Hodgkin's disease (HD) or lymphoma / malignant lymphogranuloma / granulomatous lymphoma non-Hodgkin's lymphomas / leukemias (NHL) B cells acute lymphoblastic or lymphocytic leukemia (B-ALL) mature peripheral B-cell neoplasms diffuse large B-cell lymphoma (DLBL / DLBCL) follicular center cell lymphoma (FL) mantle cell lymphoma (MCL) marginal zone B-cell lymphoma (MZL) MALT-type lymphomas (MALTomas) Burkitt's lymphoma (BL) / African lymphoma hairy cell leukemia (HCL) primary effusion lymphoma (PEL) B-cell chronic lymphocytic leukemia (B-CLL) plasma cell dyscrasias (PCD) immunocytic amyiloidosis Waldenström's macroglobulinemia (WM) monoclonal gammopathy of undertermined significance (MGUS) smoldering multiple myeloma (SMM) multiple myeloma (MM) immunoproliferative small intestine disease (IPSID) / Mediterranean lymphoma Oligoclonal lymphomas

T-cell leukemias/lymphomas T-cell acute lymphoblastic leukemia (T-ALL) T-cell large granular lymphocyte leukemia (T-LGL) aggressive NK-cell leukemia adult T-cell lymphoma / leukemia (ATL / ATLL) (HTLV-1+) peripheral T-cell lymphoma (PTCL), unspecified angioimmunoblastic T-cell lymphoma (angioimmunoblastic lymphadenopathy (AILD)-like) adult T-cell lymphoma / leukemia (ATL / ATLL) (HTLV-1+) anaplastic large cell lymphoma (T- and null cell) (ALCL) mycosis fungoides/Sézary's syndrome primary cutaneous ALCL (pcALCL) extranodal nasal/nasal type NK/Tcell lymphoma blastic NK-cell lymphoma myeloid/NK cell precursor acute leukemia enteropathy-associated T-cell-lymphoma (EATCL) subcutaneous panniculitis-like T-cell lymphoma (SCPTCL) hepatosplenic T-cell lymphoma (HTCL) mixed lineage leukemias lymphomas in the immunosuppressed patient AIDS-related lymphomas (ARL) post-transplant lymphoproliferative disorder (PTLD) Web resources

• bone marrow => intramedullary accumulation of precursors => uneffective hemopoiesis => normocytic and normochromic anemia, neutropenia, thrombocytopenia.
• thymus (thymomas)
• chronic acquired erythroblastopenia
• thymoma-associated immunodeficiency
• myasthenia gravis
• lymph nodes

• pseudoleukemia : an obsolete term for a group of conditions resembling one another in showing enlargement of the lymph glands and in characteristics which resemble the conditions present in leukemia, but without leukemic blood findings. The group included Hodgkin's disease, multiple myeloma, agnogenic myeloid metaplasia, and several other conditions.
• pseudolymphoma / lymphocytoma : a group of disorders having a benign course but exhibiting clinical and histologic features suggestive of malignant lymphoma
• Spiegler-Fendt pseudolymphoma / lymphocytoma cutis

• translocations involving LMO2, TAL2, and TAL1 in T cell acute lymphoblastic leukemia (T-ALL), are compatible with illegitimate V(D)J recombination between a TCR locus and a proto-oncogene locus bearing a fortuitous but functional recombination site (type 1)
• in contrast, translocations involving BCL1 and BCL2 in B cell non-Hodgkin's lymphomas (B-NHL), are compatible with a process in which only the IgH locus breaks are mediated by V(D)J recombination (type 2).

• French-American-British (FAB) classification : a classification of acute leukemia produced by a 3-nation joint collaboration; acute lymphocytic leukemia is subdivided into 3 types
• Revised European American Lymphoma (REAL) classification : a classification of lymphomas based on histologic criteria, dividing them into 3 main categories: B-cell neoplasms, T- or NK-cell neoplasms, and Hodgkin's disease.
• non-Hodgkin's lymphomas / leukemias (NHL) : a heterogeneous group of malignant lymphomas, the only common feature being an absence of the giant Reed-Sternberg cells characteristic of Hodgkin's disease. They arise from the lymphoid components of the immune system, and present a clinical picture broadly similar to that of Hodgkin's disease except the disease is initially more widespread, with the most common manifestation being painless enlargement of one or more peripheral lymph nodes. There have been numerous classifications of the NHLs :
• Rappaport classification (1956) : a classification of NHLs based on cytomorphology, grading, and architectural pattern (Rappaport G, Winter & Hicks EB. Follicular lymphomas. A reevaluation of its position in the scheme of malignant lymphoma, based on a survey of 253 cases. Cancer 9:792:821 (1956))
• Lukes-Collins classification (1974) : a classification of NHLs based on their presumed cells of origin. It stresses the distinction between B-cell, T-cell, and lymphocytic lymphomas, with the B-cell and T-cell types having several subtypes that can be arranged by grade of malignancy^ref
• Kiel classification (1975) : city in Germany where the pathologist Lennert developed its classification of NHLs, used primarily in Europe and based on morphologic and cytologic criteria (Lennert KK, Mohrio N, Stein H & Kaiserling E. The histopathology of malignant lymphoma. Brit. J. Hematol. 31:(suppl.1) 193-203 (1975))
• French-American-British (FAB) Cooperative Group classification for acute leukemias, 1976^ref
• Berlini's diagnosis and classification of the polycythemias, 1975^ref
• French-American-British (FAB) Cooperative Group classification for myelodysplastic syndromes, 1982^ref
• International Working Formulation (IWF) for Clinical Use (1982)^ref : a classification of NHLs based on histology and clinical parameters
• low grade NHLs (30%) :
• lymphocytic lymphoma
• follicular, predominantly small cleaved cell lymphoma
• follicular mixed small cleaved and large cell lymphoma
• intermediate grade NHLs (50%) :
• follicular, predominantly large cell lymphoma
• diffuse small cleaved cell lymphoma
• diffuse, mixed small and large cell lymphoma
• diffuse large cell lymphoma
• high grade NHLs (10%) :
• large cell immunoblastic lymphoma
• lymphoblastic lymphoma
• small non-cleaved cell lymphoma
Treatment and prognosis of NHLs :
• high and intermediate grade NHLs :
• untreated diseases have fatal prognosis with short survival measured in months
• possibility ot cure exists for a sizable portion of patients but the majority of patients develop recurrent disease after initial chemotherapy
• low grade NHLs and follicular lymphoma :
• natural history less aggressive however there is no curative treatment
• there is a pattern of repeated remissions and relapses
• median survival of low grade or follicular lymphoma is about 6.2 years
• no survival benefits from therapies
• transformed NHLs : transformation to more aggressive NHL occurs in 40-50% of patients at 5 years, 90% patients at death
Treatrment modalities of NHLs :
• chemotherapy with cytotoxic agents alone or in combination (chlorambucil, cyclophosphamide, ifosfamide with or without prednisolone or vincristine, fludarabine, cladribrine, pentostatin, mitoxantrone, paclitaxel, IFN-a or IFN-b)
• combination regimens with myeloablation
• external beam radiotherapy (EBRT)
• immunotherapy/radioimmunotherapy (RIT)
• updated Kiel classification (1988)^ref
• Polycythemia Vera Study Group (PVSG) with essential thrombocythemia, 1997^ref
• Revised European American Lymphoma (REAL) classification (1994) by the International Lymphoma Study Group (ILSG) : a classification of NHLs based on morphology, immunophenotype, genetic features, and clinical features^ref. The relative importance of each of these features varies among diseases, and there is no one 'gold standard'. In some tumors morphology is paramount, in others it is immunophenotype, a specific genetic abnormality, or clinical features. The R.E.A.L. Classification can be used by pathologists, with inter-observer reproducibility better than for other classifications (> 85%). Immunophenotyping is helpful in some diagnoses, but not required for many others. New entities not specifically recognized in the Working Formulation account for 27% of the cases. Diseases that would have been lumped together as 'low grade' or 'intermediate/high grade' in the Working Formulation show marked differences in survival, confirming that they need to be treated as distinct entities^ref.

Staging :
• I : 1 organ or lymph node (excepted mediastinum and abdomen)
• II : 1 organ and locoregional lymph nodes on the same side of diaphragm
• III : 2 organs or 2 lymph nodes on different sides of the diaphragm; primary location in mediastinum or abdomen
• IV : CNS and/or bone marrow
Onset :
• lymph nodes (60%)
• abdomen (31%)
• mediastium (26%)
• head & neck (29%)
• noncervical lymph nodes (7%)
• extranodal (40%)
• other sites (7%)
• WHO classification (2001) : based on cell type (myeloid, lymphoid T or B (with grade), histiocyte/dendritic, mast cell), this classification unifies large cell lymphomas (immunoblastic or not) and introduces anaplastic large cell lymphomas [Jaffe ES,Harris NL,Stein H,Vardiman JW, eds. World Health Organization Classification of Tumours: Pathology and Genetics of Tumours of Haematopoietic and Lymphoid Tissues. Lyon, France: IARC Press; 2001]^ref
Epidemiology : 4.4% of invasive malignancies and 4.8% of all cancer deaths; incidence and prevalence have risen 150% over the past few decades; in 2001 in USA 56,200 new cases and 26,300 deaths; incidence age-adjusted rates : 19.4 men and 12.2 women per 100,000
Aetiology :
• familial susceptibility (5%)
• extrinsic aetiology :
• toxics :
• pesticides, expecially phenoxyacids (4-11%) for CLL and FL
• solvents
• lifestyle
• tobacco smoking
• hair paints
• food
• blood transfusions
• infectious agents : there are 2 very different pathways to drive malignant lymphoproliferative diseases:
• some infectious agents activate extrinsic pathways through lymphocyte antigen receptors
• Helicobacter pylori drives the proliferation of B cells in an antigen-specific manner and treatment with anti-infective agents sometimes results in tumor regression
• HCV may similarly act through immunoglobulin receptors and may similarly respond to treatment with anti-infective agents^ref.
• others activate intrinsic pathways bypassing antigen receptors^ref
• HTLV1 drives the proliferation of infected T lymphocytes independent of the specificity of the TcR^ref
• in posttransplant lymphoproliferative disease, EBV drives lymphoproliferation independent of the specificity of the immunoglobulin. Several different EBV genes are required to act in concert to bring about this transformation, including 5 of the 6 EBV nuclear antigens.
Pathogenesis : cytogenetic translocation and associated oncogenes often seen in lymphoid malignancies  :
 

disease	cytogenetic abnormality	oncogene
B1 cells chronic lymphocytic leukemia (B-CLL)	t(14;15)(q32;q13)	-
MALT lymphoma	t(11;18)(q21;q21)	-
precursor B cell acute lymphoid leukemia	t(9;22)(q34;q11) or variant  t(4;11)(q21;q23)   BCR/ABL  AF4, ALLI
precursor acute lymphoid leukemia	t(9;22)  t(1;19)  t(17;19)  t(5;14)  BCR, ABL  E2A, PBX  HLF, E2A  IL3, IG
mantle cell lymphoma (MCL)	t(11;14)(q13;q32)	BCL-1, IgH
follicular lymphoma (FL)	t(14;18)(q32;q21)	BCL-2, IgH
diffuse large B-cell lymphoma (DLBCL)	t(3;-)(q27;-)  a  t(17;-)(p13;-)	BCL-6  p53
Burkitt's lymphoma (BL)	t(8;-)(q24;-) (numerous sites of translocation may be involved with these genes)	C-MYC
CD30+ anaplastic large cell lymphoma	t(2;5)(p23;q35)	ALK
lymphoplasmacytoid lymphoma	t(9;14)(p13;q32)	-

Symptoms & signs of patients with common types of NHLs :
 

disease	median age, years	frequency in children	% male	stage I/II vs III/IV, %	% B symptoms	% bone marrow involvement	% gastrointestinal tract involvement	% surviving 5 years
B1 cells chronic lymphocytic leukemia (B-CLL)	65	rare	53	9 vs 91	33	72	3	51
mantle cell lymphoma (MCL)	63	rare	74	20 vs 80	28	64	9	27
extranodal marginal zone B-cell lymphoma (MZL) of MALT type	60	rare	48	67 vs 33	19	14	50	74
follicular lymphoma (FL)	59	rare	42	33 vs 67	28	42	4	72
diffuse large B-cell lymphoma (DLBCL)	64	25% of childhood NHL	55	54 vs 46	33	16	18	46
Burkitt's lymphoma (BL)	31	30% of childhood NHL	89	62 vs 38	22	33	11	45
precursor T cell lymphoblastic lymphoma	28	40% of childhood NHL	64	11 vs 89	21	50	4	26
anaplastic large T/null cell lymphoma	34	common	69	51 vs 49	53	13	9	77
peripheral T cell non-Hodgkin's lymphoma	61	5% of childhood NHL	55	20 vs 80	50	36	15	25

Laboratory examinations : staging evaluation for NHL :
• physical examination
• documentation of B symptoms
• laboratory evaluation
• complete blood counts
• liver function tests
• uric acid
• calcium
• serum protein electrophoresis
• serum b₂-microglobulin
• CXR
• CT scan of abdomen, pelvis, and usually chest
• bone marrow biopsy
• lumbar puncture in lymphoblastic, Burkitt's, and diffuse large B cell lymphoma with positive marrow biopsy
• gallium scan (SPECT) or PET scan in large-cell lymphoma

• B cell leukemias / B cell lymphoproliferative disorders (BCLD) : c-Myc overrides eIF4E-induced cellular senescence and eIF4E antagonizes c-Myc-dependent apoptosis^ref. Acquired N-glycosylation sites (AGS) within tumor-specific immunoglobulin : 100% of follicular lymphomas (FL) cases present with at least one AGS, whereas the vast majority of other B-cell lymphoma types other than FL (Burkitt's lymphomas (BL), diffuse large B-cell lymphomas (DLBL / DLBCL), mantle cell lymphomas (MCL) and B-cell chronic lymphocytic leukemia (B-CLL)) do not. A second tumorigenic event?^ref. Most IgM-bearing FL cases feature their AGS within CDR2, as opposed to those bearing an IgG, which mostly display the AGS within CDR3. The vast majority of AGS located within either CDR ended with a serine residue, whereas those located within FRs mostly featured threonine as the last amino acid residue^ref. These V regions express a strikingly high incidence of N-glycosylation sequons, NXS/T. These potential glycosylation sites are introduced by somatic mutation and are lymphoma-specific, pointing to their involvement in tumor pathogenesis. Analysis of the V-region sugars from lymphoma-derived IgG/IgM reveals that they are mostly oligomannose and, remarkably, are located in the antigen-binding site possibly precluding conventional antigen binding. The Fc region contains complex glycans, confirming that the normal glycan processing pathway is intact. Binding studies indicate that the oligomannose glycans occupying the V-regions are accessible to mannose-binding lectin. These findings suggest a potential contribution to lymphoma pathogenesis involving antigen-independent interaction of sIg of the BCR with mannose-binding molecules of innate immunity in the germinal center^ref
• Hodgkin's disease (HD) or lymphoma / malignant lymphogranuloma / granulomatous lymphoma (10.5 of all BCLD; 25% of all lymphomas; incidence = 3 per 100,000 per year)
• B-cell non-Hodgkin's lymphomas/leukemias (NHL) (80% of all NHLs)
• B-cell acute lymphoblastic or lymphocytic leukemia (B-ALL) (80% of all ALL; 80% of all leukemias before age 15; prevalence = 4 per 100,000 children)
• mature peripheral B-cell neoplasms (85% of all B-NHLs)
• diffuse large B-cell lymphoma (DLBL / DLBCL) (30-50% of all B-NHLs)
• follicular center cell lymphoma (FL) (35% of all B-NHLs)
• mantle cell lymphoma (MCL) / mantle zone lymphoma / centrocytic lymphoma (5-10% of all B-NHLs)
• marginal zone B-cell lymphoma (MZL)
• nodal MZL (NMZL)
• splenic MZL (SMZL) (< 1% of NHL)
• mucosa-associated lymphoid tissue (MALT)-type lymphomas
• immunoproliferative small intestinal disease (IPSID)
• Burkitt's lymphoma (BL) / African lymphoma
• hairy cell leukemia (HCL)
• primary effusion lymphoma (PEL)
• B-cell chronic lymphocytic leukemia (B-CLL) (7% of all B-NHLs; 15 every 100,000)
Old entities :
• small or well-differentiated lymphocytic lymphoma : a diffuse form of NHL with a low grade of malignancy; it represents the neoplastic proliferation of well-differentiated B lymphocytes and may present with either focal lymph node enlargement or generalized lymphadenopathy and splenomegaly. The predominant cell type is a compact, small, normal-appearing lymphocyte with a dark-staining round nucleus, scanty cytoplasm, and little size variation. It nearly always involves the bone marrow, and often malignant cells are found in the blood, so that its clinical picture is similar to that of chronic lymphocytic leukemia
• mixed lymphocytic-histiocytic lymphoma : NHL characterized by the presence of a mixed population of cells, with the smaller cells resembling lymphocytes and the larger ones histiocytes. When predominantly follicular it is called follicular, mixed small cleaved and large cell lymphoma, and when predominantly diffuse it is called diffuse, mixed small and large cell lymphoma
• giant follicular lymphoma / giant follicle lymphoma / Brill-Symmers disease / nodular lymphoma (Brill NE, Baehr G & Rosenthal N. Generalized giant lymph follicle hyperplasia of lymph nodes and spleen. A hitherto undescribed type. JAMA 84:668 (1925); Symmers D. Follicular lymphadenopathy with splenomegaly. A new recognized disease of the lymphoid system. Arch.Pathol.3:816-870 (1927)) : any of several types of NHL in which the lymphomatous cells are clustered into identifiable nodules or follicles. The cells may be either small cleaved or large (cleaved or uncleaved) cells; tumors in which most or all of the cells are small and cleaved have a better prognosis than those with large cells

diffuse, mixed small and large cell lymphoma : a type of lymphoma that mixes the small cleaved cell and large cell varieties; it is similar to the diffuse, large cell type and has an intermediate grade of malignancy
• diffuse, small cleaved cell lymphoma : small cleaved cell lymphoma with a diffuse infiltrate of small lymphocytes that have round nuclei and clumped chromatin; this type has an intermediate grade of malignancy
• provisional entity : high-grade B-cell lymphoma, Burkitt-like (highly aggressive, high grade malignancy) (CD5^-10 / CALLA^-19⁺20⁺22⁺79a⁺, sIg^+/-, cIg^+/-)
• histiocytic lymphoma : a rare type of NHL of intermediate to high malignancy, characterized by the presence of large tumor cells that resemble histiocytes morphologically but are considered to be of lymphoid origin. Many tumors formerly placed in this category are now considered to belong in one of the large cell lymphoma groups.
• large cell lymphoma : any of several types of lymphoma characterized by the formation of malignant large lymphocytes in a diffuse pattern; some varieties contain exclusively one type of cell, such as lymphoblasts or cleaved or uncleaved follicular center cells, and others have a mixture of cells, sometimes including ones that cannot be characterized as to lineage
• large cleaved cell lymphoma : a type of NHL characterized by the formation of malignant large cleaved follicular center cells; there are both follicular and diffuse varieties. Because of the wide variety of prognostic levels and the existence of tumors with several types of cells, these tumors have been divided among several different groups of follicular and diffuse lymphomas.
• large noncleaved cell lymphoma : a type of NHL characterized by the formation of malignant large noncleaved follicular center cells. Because of the wide variety of prognostic levels and the existence of tumors with several types of cells, these tumors have been divided among several different groups of follicular and diffuse lymphomas.
• large cell, immunoblastic lymphoma : a type of NHL characterized by large lymphoblasts (immunoblasts : few organelles, abundant RER, lack of glycogen granules and membrane specializations) that resemble histiocytes rather than follicular center cells, and have a diffuse pattern of infiltration; the cell population may be exclusively B or T lymphoblasts or a mixture. It has a high degree of malignancy and often grows rapidly. Tumors of predominantly B cells are often associated with a preexisting immunologic disorder such as Sjögren's syndrome, systemic lupus erythematosus, or Hashimoto's thyroiditis or with an immunosuppressed state.
• immunoblastic sarcoma of B cells : large cell, immunoblastic lymphoma composed predominantly of B cells
• small B-cell lymphoma : the usual type of small lymphocytic lymphoma, having predominantly B lymphocytes
• small cleaved cell lymphoma : a group of NHL characterized by the formation of malignant small cleaved follicular center cells; it may have either a follicular or a diffuse pattern. One type, called follicular, predominantly small cleaved cell lymphoma, is particularly common. Because of the wide variety of prognostic levels and the existence of tumors with several types of cells, these tumors have now been divided among several different groups of follicular and diffuse lymphomas.
• small noncleaved cell lymphoma : any of several types of lymphoma characterized by the formation of malignant large lymphocytes in a diffuse pattern; some varieties contain exclusively one type of cell, such as lymphoblasts or cleaved or uncleaved follicular center cells, and others have a mixture of cells, sometimes including ones that cannot be characterized as to lineage
Symptoms & signs : lymphoma cutis (primary skin involvement by B-cell lymphoma without demonstrable systemic disease, most often presenting as a solitary, purple to pink nodule, especially on the head, neck, and face, and usually associated with dissemination to regional lymph nodes and distant hematogenous spread, leading to widespread involvement)
Web resources : Immunogenetics in Defining B-Cell Malignancy by Surinder S. Sahota
• plasma cell dyscrasias (PCD) / monoclonal gammopathies or immunoglobulinopathies / dysproteinemias / paraproteinemias : a diverse group of neoplastic diseases involving proliferation of a single clone of cells producing a serum M component (a monoclonal immunoglobulin or immunoglobulin fragment); the cells usually have plasma cell morphology, but may have lymphocytic or lymphoplasmacytic morphology
• gammopathy : a condition marked by disturbed immunoglobulin synthesis.
• immunocytic amyiloidosis (incidence = 8 per 1,000,000 per year)
• non-Hodgkin's lymphomas (NHL)
• Waldenström's macroglobulinemia (WM) (prevalence = 2% of all hematological malignancies)


• smoldering multiple myeloma (SMM) (incidence = 15% of newly diagnosed MM)
• monoclonal gammopathy of uncertain (or undertermined) significance (MGUS) (prevalence = 3 per 100)
• multiple myeloma (MM) (incidence = 5-10 per 100,000 per year)
• heavy chain diseases (HCD) : a group of rare malignant neoplasms of lymphoplasmacytic cells that secrete an M component consisting of monoclonal immunoglobulin heavy chains or heavy chain fragments; they are classified according to heavy chain type
• g heavy chain disease (g-HCD) / Franklin disease : a heavy chain disease occurring usually in elderly persons that clinically resembles a malignant lymphoma

Symptoms & signs : lymphadenopathy, hepatosplenomegaly, and recurrent infections
Laboratory examinations : leukopenia and often eosinophilia
• a heavy chain disease (a-HCD) / Seligmann disease : the most common heavy chain disease, occurring predominantly in young adults in the Mediterranean area, and characterized by ...
• immunoproliferative small intestine disease (IPSID) / Mediterranean lymphoma
• pulmonary involvement (exceedingly rare)
• m heavy chain disease (m-HCD) : the rarest heavy chain disease, found in patients with chronic lymphocytic leukemia

Symptoms & signs : hepatomegaly and splenomegaly
• d heavy chain disease (d-HCD)
• germinotropic lymphoproliferative disorder (GLD) :

Aetiology : HHV-8 / KSHV⁺ lymphocytes in GLD are co-infected by HHV-4 / EBV and most of them also expressed vIL-6, which is much higher than that in PEL and KSHV-associated MCD (10%-20%)^{ref1, ref2}. Activation of IL-6R signaling through vIL-6 and human IL-6 may play an important role in this disease as in PEL and KSHV-associated MCD^{ref1, ref2, ref3}. Nonetheless, the pathogenic potential seems to be constrained by a competent immune system. Unexpectedly, molecular analysis of whole tissue sections or microdissected KSHV⁺ aggregates demonstrated a polyclonal or oligoclonal pattern of Ig gene rearrangement. The plasmablasts showed somatic mutation and intraclonal variation in the rearranged Ig genes, and one case expressed switched Ig heavy chain (IgA), suggesting that they originated from germinal center B cells. Plasmablasts that preferentially involved germinal centers of the lymphoid follicles, forming confluent aggregates. CD10^-20^-27^-30^+/-38^+/-79a^-138^-BCL6^- but showed monotypic k or l light chain^ref. Clusters of CD10⁺20⁺ residual follicle center cells were identified in some of the follicles^ref
Symptoms & signs : localized lymphadenopathy
Therapy : favorable response to chemotherapy or radiotherapy.
Pathogenesis : AID makes no measurable contribution to the generation of initial translocations involving immunoglobulin heavy chain (Igh) switch regions and an oncogene such as c-MYC, indicating that the intrinsic fragility of the switch regions or a pathway unrelated to AID is responsible for these translocations. In contrast, the outgrowth of translocation-positive cells is dependent on AID, raising the possibility that AID is important in tumor progression, perhaps by virtue of its mutagenic properties^ref. PCL showed significantly less immunostaining for CD27 (P < .01) and p27 (P < .05) compared with plasmacytoma and multiple myeloma. Low CD27 expression also was associated with plasmacytoma progression to multiple myeloma (P <.05)^ref
Laboratory examinations :
• M component / paraprotein [for myeloma or macroglobulinemia] is an abnormal monoclonal immunoglobulin with a characteristic electrophoretic pattern, occurring in the serum of patients with PCDs and formed by the proliferating concentrations of immunoglobulin-producing cells
• autoimmune hemolytic anemias
Summary of lymphomagenesis : the neoplastic cells of B-cell and T-cell lymphomas express the differentiation antigens characteristic of normal lymphocyte subsets, and the genetic changes in most B-cell lymphomas recapitulate the alterations in the immunoglobulin genes that take place during normal B-cell development. Moreover, the molecular pathogenesis of B-cell lymphomas is often related to perturbation of a normal physiological event. For example, most B-cell lymphomas are characterized by translocations of the immunoglobulin genes or other genes critical to B-cell development, such as BCL6. These alterations appear to occur as mistakes in the normal recombination or somatic mutation processes^{ref1, ref2}. The rationale for such a classification of B-cell lymphomas is based on the observation that malignant B cells seem to be &lsquo;frozen&rsquo; at a particular differentiation stage, which reflects their origin^{ref1, ref2, ref3}. One of the main concepts emerging from these studies is that most types of B-cell lymphoma are derived from GC or post-GC B cells^{ref1, ref2}. The cellular origin of B-cell lymphomas was further clarified, and previously unrecognized distinct lymphoma subtypes were also identified, by gene-expression profiling of human B-cell lymphomas and normal B-cell subsets. Such studies identified, for example, a GC B-cell gene-expression signature that is associated with follicular lymphoma, Burkitt&rsquo;s lymphoma and a subset of diffuse large B-cell lymphomas^ref. These findings supported the GC B-cell origin of these tumours. Gene-expression profiling studies of other malignancies also revealed
unexpected relationships, in terms of gene-expression patterns. For example, in addition to B-cell chronic lymphocytic leukaemia (B-CLL) cells with mutated Ig variable (V)-region genes, B-CLL cells with unmutated Ig V-region genes showed greatest similarity to memory B cells that had undergone somatic hypermutation, indicating that both subtypes of B-CLL are related to memory B cells^ref. Moreover, a subset of diffuse large B-cell lymphomas was identified that, among the various B-cell subsets included in the analysis, most closely resembled in-vitro-activated B cells^ref. In these cancer cells, the transformation process might have been associated with an alteration of the gene-expression profile, masking the signature of the cell of origin, as seems to be the case in classical Hodgkin&rsquo;s lymphoma. It is also possible that the normal B-cell counterpart of some cancer types might not have been identified yet. In the activated B-cell type of diffuse large B-cell lymphoma,the normal counterpart could be a poorly defined, small subset of GC B cells that is undergoing plasmacytoid differentiation, or a post-GC immunoblast population^ref. Reciprocal chromosomal translocations involving one of the Ig loci and a proto-oncogene are a hallmark of many types of B-cell lymphoma^{ref1, ref2}. As a consequence of such translocations, the oncogene comes under the control of the active Ig locus, causing a deregulated, constitutive expression of the oncogene. 3 types of breakpoints can be distinguished in the Ig loci. Some translocations, such as the BCL2-IgH translocationassociated with follicular lymphoma, have breakpoints that are directly adjacent to Ig heavy chain J-region (J_H) gene segments or that are adjacent to regions where the Ig heavy chain D-region (D_H) joins the J-region (D_HJ_H). As the breakpoints also often show loss of nucleotides at the end of the J_H or D_H segments and the addition of non-germline-encoded nucleotides - typical features of V(D)J recombination - it is likely that these translocations happen as mistakes during V(D)J recombination in early B-cell development in the bone marrow^{ref1, ref2, ref3}. In other translocations, the breakpoints are found within or adjacent to rearranged V(D)J genes, and these V-region genes are always somatically mutated. These and additional features indicate that such translocations occur as by-products of the somatic hypermutation process^{ref1, ref2}, which is associated with DNA strand breaks^{ref1, ref2, ref3}. The third type of translocation is characterized by breakpoints in the IgH constant region switch regions, in which DNA breaks are introduced during class switching. This indicates that these events occur during class-switch recombination. The causes for the generation of DNA strand breaks in the oncogenes involved in Ig-associated translocations are less clear^ref. Some of these genes, however, undergo aberrant somatic hypermutation, and therefore acquire DNA strand breaks in the same regions where the chromosomal breakpoints are located^ref. Regarding the BCL2-IgH translocations associated with follicular lymphoma, it was recently shown that the DNA in the major breakpoint region of the BCL2 gene often acquires an altered structure that is cut by the RAG nucleases, which mediate V(D)J recombination. This finding indicates that in these translocations, RAG-mediated DNA cleavage is responsible for the DNA breaks in both partners involved in the translocation^ref. RAG enzymes might also be involved in chromosomal translocations through another mechanism - RAGs have been shown to possess transposase activity, so some translocation events could be explained by double-ended transposition events^{ref1, ref2}. The process of somatic hypermutation contributes to lymphoma pathogenesis not only by causing chromosomal translocations, but probably also by targetingnon-Ig genes. 2 situations have to be distinguished. The genes encoding BCL6 and CD95 (also known as FAS) were found to contain mutations in a considerable fraction of normal GC and memory B cells, indicating that these genes are often targeted by the hypermutation machinery in normal B cells^{ref1, ref2, ref3}. In rare instances, such mutations might promote the development of lymphomas. For example, inactivating mutations of CD95 are found in about 20% of (post) GC B-cell lymphomas and could protect lymphoma cells from death induction by CD95-ligand-expressing cells^ref. In the case of the BCL6 gene, the frequent occurrence of hypermutation might also cause translocations of this gene into Ig- as well as non-Ig-encoding loci. This possibility was indicated by the finding that the 5' region of BCL6, which is the site of hypermutation, is also the region where chromosomal-translocation breakpoints are mostly found^{ref1, ref2}. In diffuse large B-cell lymphomas, aberrant hypermutation of multiple oncogenes has been reported, which might also represent an important mechanism of pathogenesis^ref. 2 of the molecular processes that could cause chromosome translocations or mutations in non-Ig genes occur exclusively (or at least mainly) in the GC - somatic hypermutation and class-switch recombination^ref . This could be one of the reasons that most B-cell lymphomas derive from GC B cells or their descendents. Class switching and somatic hypermutation do not occur in the DNA of T cells, which could also partly explain why B cells are more prone to undergo malignant transformation than T cells. Whereas chromosome translocations involving Ig loci are clearly a hallmark of many types of B-cell lymphoma, many other transforming events have also been implicated in the pathogenesis of lymphomas, such as mutations in tumour-suppressor genes (such as TP53 and the gene encoding IkBa), genomic amplifications such as REL) and translocations not involving Ig loci (API2-MALT1). Finally, viruses might also be involved in the transformation of B cells. The most well-known example is Epstein-Barr virus (EBV), which is found in nearly all endemic Burkitt&rsquo;s lymphomas, in many post-transplant and primary effusion lymphomas, and in about 40% of cases of classical Hodgkin&rsquo;s lymphoma^{ref1, ref2, ref3} (Rickinson, A. B. & Kieff, E. Epstein-Barr virus. in Fields Virology (eds Knipe, D. M. & Howley, P. M.) 2575-2627 (Lippincott-Raven, Philadelphia, 2001)). Another member of the herpes-virus family, human herpes virus 8, is implicated in the pathogenesis of primary effusion lymphomas^ref. The oncogenic features of herpes virus 8 are not well understood, but it was recently shown that the viral protein FLIP activates the transcription factor NF-kB, which is an important survival factor in primary effusion lymphoma cells^ref. Role of the BCR in B-cell lymphomas Role of the BCR in the survival of normal B cells. Throughout their lives, B cells undergo stringent selection for expression of the appropriate BCR. Pre-B cells are selected for a pre-BCR (composed of Ig heavy chains and surrogate light chains), and immature B cells are selected for expression of a non-autoreactive, functional BCR.After these steps, GC B cells are only able to survive the GC reaction and differentiate into memory or plasma cells if somatic mutations in their V-region genes result in expression of a BCR with increased affinity for a cognate antigen^ref. Even mature resting B cells are constantly under selective pressure to express the BCR - ablation of BCR expression in mice leads to the apoptotic death of BCR-negative B cells^{ref1, ref2}. So, it seems that this BCR dependency is a main determinant of B-cell survival. It is still debated whether the survival signal supplied by the BCR is an autonomous signal or is initiated by low-level BCR activation by antigen. BCR dependency of B-cell lymphomas. The selection for expression of a BCR also seems to occur in malignant B cells. Indeed, most B-cell lymphomas still express a BCR, although sometimes at relatively low levels^{ref1, ref2, ref3}. The proposal that there is a need for BCR-derived survival signals is indirectly supported by the observation that translocations into the Ig-loci are virtually always found on the non-productively rearranged Ig loci,with a few exceptions^ref. As the 3 Ig-gene-remodelling processes that are implicated in the generation of these translocations - V-region gene recombination, class switching and somatic hypermutation - principally occur in both Ig alleles, translocation events should happen at nearly equal frequency on the expressed Ig allele and the non-expressed allele. However, as the expressed Ig alleles are not found to be inactivated by translocation events, it seems that at least at the time that the translocations happened, the inability to form a BCR was incompatible with survival of the cells and development into a B-cell tumour. Further evidence that the BCR supplies important survival signals to B-cell lymphoma cells is provided by the observation that treatment of patients who have follicular lymphoma with Anti-idiotypic antibodies did not result in the emergence of BCR-negative lymphoma variants - either through downregulation of BCR expression or by selected outgrowth of clones with inactivating Ig V-region gene mutations^{ref1, ref2}. Finally, several types of lymphoma show ongoing V-region gene mutation during tumour clone expansion^{ref1, ref2, ref3, ref4, ref5}. As a considerable fraction of mutations would interfere with BCR expression or function, such as nonsense mutations or replacement mutations that prevent proper heavy- and light-chain pairing, it is notable that such lymphomas also retain BCR expression^{ref1, ref2}. Indeed, it has been determined that two types of destructive somatic mutation - nonsense mutations and deletions or duplications causing reading-frame shifts - account for nearly 10% of mutation events, if mutations accumulate under non-selective conditions^{ref1, ref2}. So, the rare occurence of BCR-loss variants of lymphomas with ongoing somatic hypermutation, such as follicular lymphoma, Burkitt&rsquo;s lymphoma, lymphocyte-predominant Hodgkin&rsquo;s lymphoma or mucosa-associated lymphoid tissue (MALT) lymphomas, is a strong indication that lymphoma cells undergo selection for BCR expression. Therefore, the survival signals supplied by BCR expression in normal B cells might also promote survival of B-cell lymphoma cells. Exceptional B-cell lymphomas that do not express the BCR. Although evidence is strong that most B-cell lymphomas depend on BCR expression, there are a few exceptions. In classical Hodgkin&rsquo;s lymphoma, inactivating Ig V-region gene mutations that render originally functional V-region gene rearrangements non-functional were detected in 25% of cases^{ref1, ref2}. As only a small fraction of inactivating mutations that occur in mutating GC B cells can easily be identified (for example, nonsense mutations and deletions), it is possible that Hodgkin and Reed-Sternberg (HRS) cells - the tumour cells in patients with classical Hodgkin's lymphoma - in most if not all cases are derived from pre-apoptotic GC B cells that have lost the capacity to express high-affinity BCR. How can HRS cells escape selection to evade apoptosis? In about 40% of cases of classical Hodgkin&rsquo;s lymphoma, HRS cells are infected by EBV and express the EBVencoded latent membrane protein 2A (LMP2A) (Rickinson, A. B. & Kieff, E. Epstein?Barr virus. in Fields Virology (eds Knipe, D. M. & Howley, P. M.) 2575-2627 (Lippincott-Raven, Philadelphia, 2001)). LMP2A harbours an immunoreceptor tyrosine-based activation motif, which is also found in the CD79A and CD79B (also known as Iga and Igb, respectively) molecules of the BCR and is required for BCR-mediated survival signalling^ref. Studies of transgenic mice that express LMP2A in B cells have shown that LMP2A expression can replace the BCR-mediated signals^{ref1, ref2}. So, expression of LMP2A in an EBV-infected GC B cell that is undergoing hypermutation might rescue the cell from apoptosis following acquisition of unfavourable somatic V-region gene mutations. After acquisition of additional transforming events (other than EBV infection), that cell could, in rare instances, give rise to an HRS tumour clone^ref. The role of LMP2A in the established HRS cell clone, however, is less clear, because HRS cells have downregulated expression of central components of the BCR signalling cascade^ref, including spleen tyrosine kinase (SYK) and SLP65, which seem to be essential for the function of LMP2A as a BCR surrogate^{ref1, ref2}. Indeed, HRS cells have lost expression of nearly all B-cell-typical genes^{ref1, ref2, ref3}. Whether this &lsquo;lost B-cell phenotype&rsquo; is directly related to pathogenesis and/or the presumed derivation from crippled GC B cells is unclear. Perhaps, for a GC B cell,which because of disadvantageous somatic mutations does not receive appropriate survival signals and would therefore normally undergo apoptosis, it is advantageous to lose its B-cell identity as a means of becoming independent from the stringent selection for expression of a (highaffinity) BCR. Such a phenotypic change might be promoted by, or depend on, transforming events involved in HRS-cell generation.Alternatively, the loss of the B-cell phenotype might be largely unrelated to derivation from crippled GC B cells, and might instead reflect transforming events in HRS-cell pathogenesis that render the cells independent from expression of a BCR. As a consequence, the HRS cells would no longer be under selective pressure to maintain their B-cell-specific xpression programme and could adopt another phenotype. Lymphoma clones with inactivating V-region gene mutations have also been observed in a fraction of cases of post-transplant lymphomas^{ref1, ref2, ref3}. These are usually EBV⁺ and express all latent EBV genes, so it is possible that LMP2A promotes the survival of these crippled lymphoma cells. The requirement for BCR expression is unclear in primary mediastinal B-cell lymphomas. These lymphomas lack detectable BCR expression and have downregulated expression of components of the BCR signalling cascade and activity of the internal IgH enhancer, but no samples with inactivating V-region gene mutations have been described^{ref1, ref2, ref3}. Recent gene-expression studies revealed, surprisingly, that primary mediastinal B-cell lymphomas are in many aspects closely related to HRS cells of classical Hodgkin&rsquo;s lymphoma,and are more similar to this lymphoma than to other diffuse large B-cell lymphomas. But unlike Hodgkin&rsquo;s lymphoma, mediastinal lymphomas have largely retained a B-cell gene-expression pattern and are not associated with EBV infection^{ref1, ref2}. In the rare primary effusion lymphomas, BCR expression is usually very low or undetectable, but no cases with inactivating mutations have been reported^{ref1, ref2, ref3}. Notably, these lymphomas also lack expression of the transcription factors PU.1,OCT2 and BOB1, which are important regulators of Ig transcription^ref. The loss of these transcription factors could explain the downregulation of Ig expression in primary effusion lymphoma cells. These lymphomas also usually lack detectable expression of other B-cell markers, such as CD19 and CD20, indicating a loss of the B-cell phenotype in the effusion lymphomas that is similar to that of classical Hodgkin&rsquo;s lymphomas, although several aspects of their phenotype are also compatible with a plasmablastic differentiation^ref. Antigen activation of B-cell lymphomas Is the ability of the BCR to transmit survival signals, or its ability to interact with antigen to activate lymphocyte proliferation, required for lymphomagenesis? Studies in several different lymphoma types have indicated that lymphoma cells recognize antigen, and that stimulation by antigen binding contributes to survival and proliferation of lymphoma cells. This concept was first proposed > 40 years ago^ref. In B-CLL cells, the BCR has been frequently shown to bind autoantigens^{ref1, ref2}. In some cases, however, B-CLL cells show specificity for foreign antigens, such as viral proteins - this is the case in B-CLL that is positive for human T-lymphotropic virus type I. Moreover, seven subgroups of B-CLL have recently been identified that show strikingly similiar V_H and V_L gene-rearrangement sequences among members of a group^{ref1, ref2, ref3, ref4}. Although it is possible that this finding is due to derivation of the lymphoma cells from a so-farunrecognized B-cell subset with a highly restricted V-region gene repertoire, it is more likely that this reflects selection and activation of these cases by a restricted set of antigenic epitopes. In line with this view, 5 of the 7 groups identified belong to the subclass of unmutated B-CLL, which has a phenotype reminiscent of antigen-activated B cells^ref. Restricted V-region gene usage is also a hallmark of primary central nervous system lymphoma.However, unlike the situation with B-CLL, this restriction only holds true for the expressed V_H gene segment, which is the same in about half of the cases^{ref1, ref2}. This binding of an antigen exclusively to the V_H gene segment, and that antigen might therefore be a superantigen. So, stimulation of B cells by a superantigen might be involved in the pathogenesis of primary central nervous system lymphomas. Studies also indicate a role for antigen activation in the pathogenesis of follicular lymphoma. First, lymphoma cells from several patient samples were found to express BCR with autoreactivity^ref. Second, follicular lymphoma cells show ongoing somatic hypermutation during tumour-clone expansion, and the pattern of these mutations is indicative of their selection by antigen^ref. Third, about 80% of follicular lymphomas carry somatic V-region gene mutations that result in the generation of carbohydrate-linking motifs^ref. Such mutations were also found at a similar frequency in endemic Burkitt&rsquo;s lymphoma, but are present in < 10% of cases of multiple myeloma, MALT lymphoma or normal B cells^{ref1, ref2}. The strong selection for the acquisition of carbohydrate modifications to the BCR V region of follicular and endemic Burkitt&rsquo;s lymphoma cells indicates that these moieties are important for lymphoma formation. It is unclear whether the carbohydrates are involved in the recognition of antigens or in the interaction of the lymphoma cells with stromal elements. Hepatitis C virus (HCV)-associated B-cell lymphomagenesis has been associated with viral antigens. One study demonstrated the direct binding specificity of the BCR for a viral-envelope protein^ref. Importantly, treatment of several patients with HCV-associated splenic B-cell lymphomas with anti-viral interferon therapy not only eliminated the virus, but also caused regression of the lymphoma^ref. The fact that several HCV-unrelated splenic B-cell lymphomas did not respond to interferon therapy supports the idea that the regression of the lymphoma is indeed caused by the elimination of the stimulating antigen, rather than sensitivity of the lymphoma cells themselves to interferon^ref. Foreign antigen seems to have an indirect role in activating B-cell-lymphoma clones in gastric MALT lymphomas. Here, nearly all cases are associated with chronic infection of the gastric mucosa by the bacterium Helicobacter pylori^ref. However, it is not the lymphoma cells that recognize the bacterium, but T-helper cells, which stimulate the proliferation of the lymphoma cells^ref. Notably, some studies have indicated that the lymphoma B cells recognize autoantigen(s)^{ref1, ref2}, and a recent analysis showed that a considerable fraction of gastric and salivary-gland MALT lymphomas (20-40% of cases) express autoantibodies with specificity for IgG (that is, rheumatoid factors)^ref. Foreign and autoantigens therefore seem to synergize in the pathogenesis of gastric MALT lymphomas. Role of the lymphoma microenvironment In many lymphomas, the tumour microenvironment is likely to be important for the survival and/or proliferation of the tumour cells. In follicular lymphoma, the tumour cells reside and proliferate in follicular structures in close association with T-helper cells and follicular dendritic cells, as is typical for normal GC B cells. Some B cells belonging to the lymphoma clone can also be found in the interfollicular areas, but these cells show little proliferative activity^ref. So, the lymphoma cells seem to require the cellular interactions in the GC-like environment for their proliferation. This is supported by studies that showed that follicular lymphoma cells can proliferate in vitro only if they are cultured together with CD4⁺ T cells, or with stromal cells and an antibody against the CD40 receptor^{ref1, ref2}.CD40 is expressed by follicular-lymphoma cells, and its activation is a main survival signal for normal GC B cells. Notably, it was recently shown that the survival of patients with follicular lymphoma is correlated with characteristic features of non-tumour cells in the lymphoma tissue^ref. So, it seems that follicular lymphoma cells retain key features of normal GC B cells, including the dependency on BCR expression and activation, as well as the interaction with T cells and follicular dendritic cells in the follicular microenvironment. Low-grade gastric MALT lymphomas also depend on the interaction with tumour-infiltrating T cells.These lymphomas are closely associated with H. pylori infection. In vitro, H. pylori stimulates the proliferation of tumour-infiltrating T cells, but not of the lymphoma B cells directly^{ref1, ref2}. These T cells then provide contactdependent help to promote the survival and proliferation of the lymphoma cells^ref. The fact that elimination of H. pylori by antibiotic treatment often leads to regression of the lymphoma highlights the importance of this interaction in lymphoma progression^ref. In B-CLL, the leukaemic cells in the peripheral blood show very little proliferative activity, indicating that the expansion of the tumour clone might take place in other tissues affected by the lymphoma. Indeed, proliferation of B-CLL cells is largely restricted to proliferation centres in lymph nodes and bone marrow, where the cells are in intimate contact with CD4⁺ T cells and dendritic cells^ref. The in vitro survival of B-CLL cells can be significantly extended by culturing the leukaemic cells with stromal cells, and B-CLL cell proliferation can be induced by triggering the CD40 receptor^{ref1, ref2}. As CD40L is expressed by a fraction of T cells in the proliferation centres^ref, it is intriguing to speculate that the T cell-B-CLL interaction in that particular microenvironment provides important survival and proliferation signals for the malignant clone. Histological analyses of classical Hodgkin&rsquo;s lymphoma cells have also indicated an important role of the cellular microenvironment in the pathogenesis of this B-cell malignancy. The HRS cells usually account for < 1% of cells in the tumour tissue, and most of the cellular infiltrate is composed of T cells, eosinophils, macrophages, B cells, plasma cells and other cells. Although this cellular infiltrate could partly represent an (unsuccessful) inflammatory response against the HRS cells, there is evidence that at least a large fraction of the non-tumour cells is actively attracted by the HRS cells. For example, HRS cells attract CD4⁺ T cells by the secretion of large amounts of the cytokine TARC (thymus and activation-regulated chemokine), which is normally only expressed by dendritic cells^ref. Indeed, HRS cells  are usually in direct contact with T-helper cells. Importantly, although HRS cells have lost expression of most B-cell-specific genes, molecules important for interaction with T-helper cells (major histocompatibility complex class II, CD40, CD80 and CD86) are still expressed^ref, indicating that this interaction with CD4+ T cells is important for the survival of the HRS cells. The dependency of HRS cells on their typical microenvironment is further supported by the difficulty of maintaining these cells in culture, by the inability of primary HRS cells to survive in immunodeficient mice, and by the observation that HRS cells only rarely disseminate to the peripheral blood^ref. Implications and future directions In an emerging picture of B-cell malignancy, tumour progression not only depends on transforming events, such as chromosomal translocations, but also on survival signals mediated by the expression of a functional BCR and cellular interactions in the lymphoma microenvironment. In many lymphomas, BCR binding of foreign or autoantigens to stimulate proliferation might also be involved.Other than pathogen-derived antigens that cause chronic infections, certain autoantigens can also stimulate reactive B cells. This concept is also supported by the observation that several autoimmune diseases, such as Sjogren&rsquo;s syndrome, rheumatoid arthritis and autoimmune lymphoproliferative syndrome are commonly associated with an increased risk of lymphoma^{ref1, ref2}. Moreover, autoantigen specificity for the BCR expressed by the lymphoma has been reported for some patients with autoimmune disease who developed lymphoma^ref. However, it could be that in some cases, antigen activation provides a chronic proliferative stimulus to B cells that only increases their risk of malignant transformation, and that antigen activation does not have an important role in progression ofestablished lymphomas.The finding that many lymphomas seem to arise from B-cell precursors that were &lsquo;frozen&rsquo; at a particular stage of differentiation could reflect key features of lymphoma pathogenesis. For example, lymphoma-associated translocations that disrupt the BCL6 gene result in constitutive expression of this transcription factor, keeping the cells in a proliferative, GC B-cell-like stage, and prevents their differentiation into a resting post-GC B-cell stage. The dependency of lymphomas on BCR expression, antigen triggering and microenvironmental survival signals might contribute to the relatively close similarity between many B-cell lymphomas and their normal B-cell counterparts in terms of phenotype and gene-expression pattern. The dependency on such factors would select for a tumour phenotype that still resembles normal B cells in many aspects. In other instances, if the transforming events release the cells from such a dependency, the lymphoma cells would be free to acquire a markedly different phenotype. This might be best exemplified in classical Hodgkin&rsquo;s lymphoma, where the BCR-deficient HRS cells have lost most features of normal B cells. Can new treatment options for B-cell lymphomas be developed from our current understanding of the role of the microenvironment in lymphoma progression and of antigen as the driving force for proliferation of lymphoma cells? Lymphomas might be treated by unconventional approaches, such as by interfering with survival or proliferation signals from other cells in the lymphoma microenvironment, by eliminating antigens that promote expansion of tumour cells, or by interfering with the BCR signalling pathway. The success in treating patients with H. pylori-associated gastric MALT lymphomas, or patients with HCV-associated B-cell lymphomas, by eliminating the infectious agents are the first promising examples of this approach. Finally, the gene-expression profiling studies of lymphomas might reveal previously unrecognized mechanisms of pathogenesis in B-cell lymphomas that could lead to novel therapeutic strategies. For example, the recognition that a subtype of diffuse large B-cell lymphoma expresses an active NF-kB signature led to the identification of a dependency of these lymphomas on constitutive NF-kB activity -making this transcription factor an attractive target for therapy^ref.


• pro-B cell => B1 acute lymphoblastic leukemia
• pre-B cell => B3 acute lymphoblastic leukemia
• mature naive B-cell =>
• B4 acute lymphoblastic leukemia
• [plasmablastic multicentric Castleman's disease (MCD)]
• mantle zone B-cell => mantle cell lymphoma (MCL) / mantle zone lymphoma / centrocytic lymphoma

The presence of somatic mutations characterizes the neoplastic cells as being at either a germinal-center or a post-germinal center stage of differentiation.
• germinal centre B cell (Ig mutations) =>
• follicular center cell => follicular center cell lymphoma (FL) => secondary ...
• de novo germinal center B-cell like (GCB) diffuse large B-cell lymphoma (DLBL / DLBCL)
• B1 cells chronic lymphocytic leukemia (B-CLL)
• Burkitt's lymphoma
• Hodgkin's disease (HD)
• germinotropic lymphoproliferative disorder (GLD)
• AIDS-related body cavity-based B-cell primary effusion lymphomas (PEL) (?)
• memory B cells => Burkitt's lymphoma
• post-germinal centre B-cell =>
• marginal zone B-cell => marginal zone B-cell lymphoma (MZL)
• MALT-type lymphomas (MALTomas)
• plasma cell => multiple myeloma
• activated B-cell-like (ABC) diffuse large B-cell lymphoma (DLBL / DLBCL)
• AIDS-related body cavity-based B-cell primary effusion lymphomas (PEL) (?)
B-cell chronic lymphoproliferative disorders (B-CLPDs) are a heterogeneous group of diseases that result from the proliferation and accumulation of mature-appearing aberrant B lymphocytes arrested at a given stage of differentiation^{ref1, ref2, ref3} (Orfao A, Almeida J, Sanchez ML, San Miguel JF. Immunophenotypic diagnosis of leukemic B-cell chronic lymphoproliferative disorders other than CLL. In: Guy B. Faguet, ed. Chronic Lymphocytic Leukemia: Molecular Genetics, Biology, Diagnosis and Management. Totowa, NJ: Humana Press; 2003: 173-190; Matutes E, Worner I, Sainati L, de Oliveira MP, Catovsky D. Advances in the lymphoproliferative disorders: review of our experience in the study of over 1000 cases. Biol Clin Hematol. 1989;11: 53-62)1-5 B-CLPDs are generally believed to result from the monoclonal expansion of a single transformed B lymphocyte (Fialkow PJ. Clonal and stem cell origin of blood cell neoplasms. In: Lobue J, Gordon AS, Silber R, Muggia FM, eds. Contemporary Hematology/Oncology. Plenum Publishing; New York, NY; 1980: 1-46). Therefore, the tumoral B lymphocytes constitute a clone in which all cells are related by possessing the original transforming mutation, possessing identical VDJ rearrangements of the immunoglobulin heavy chain (IgH) gene, and showing restricted Ig light chain expression. Additionally, distinctive genetic and phenotypic features may be gained during the evolution of the disease. In this sense, the presence of 2 or more morphologically different populations of neoplastic lymphocytes in the same patient, detected either simultaneously or at different time points, is usually interpreted as reflecting either different maturation stages or subclone formation within the original malignant tumor stem cell line^ref. Although most lymphoproliferative disorders are considered to be monoclonal, biclonality has been occasionally reported in the literature^{ref1, ref2, ref3, ref4, ref5, ref6, ref7, ref8, ref9, ref10, ref11, ref12}, frequently corresponding to rare cases of B-cell non-Hodgkin lymphomas (NHLs), which more commonly develop in immunocompromised individuals^{ref1, ref2, ref3, ref4}. In most instances these reports describe the coexistence of 2 distinct diseases such as mantle cell lymphoma (MCL) and follicular lymphoma (FL)^ref, follicular lymphoma (FL) and B-cell chronic lymphocytic leukemia (B-CLL)^ref, mantle cell lymphoma (MCL) and B-cell chronic lymphocytic leukemia (B-CLL)^ref, B-cell chronic lymphocytic leukemia (B-CLL) and diffuse large B-cell lymphoma (DLBCL)^ref, and hairy cell leukemia (HCL) and B-cell chronic lymphocytic leukemia (B-CLL)^ref. Therefore, these cases would not correspond to oligoclonal expansions of B cells, which have long been claimed to precede the monoclonal disease state^ref. B-CLPDs are a group of diseases characterized by the proliferation of mature-appearing B cells, which are generally believed to result from the monoclonal expansion of a single transformed precursor cell (Orfao A, Almeida J, Sanchez ML, San Miguel JF. Immunophenotypic diagnosis of leukemic B-cell chronic lymphoproliferative disorders other than CLL. In: Guy B. Faguet, ed. Chronic Lymphocytic Leukemia: Molecular Genetics, Biology, Diagnosis and Management. Totowa, NJ: Humana Press; 2003: 173-190). In fact, in B-CLPD oligoclonality has been usually related to the development of new B-cell subclones resulting from the occurrence of additional genetic abnormalities on the neoplastic cells along the evolution of the disease^{ref1, ref2}; reports on B-CLPD cases with 2 or more distinct unrelated B-cell clones are scanty in the literature and restricted to between 1 and 3 patients at maximum^{ref1, ref2, ref3, ref4, ref5, ref6, ref7}. In most of these cases, biclonality was suspected based on flow cytometry immunophenotypic studies, which revealed the presence of 2 phenotypically distinct B-cell populations^{ref1, ref2}, frequently displaying a different sIg light chain isotype^{ref1, ref2, ref3, ref4, ref5}; molecular analysis confirmed the presence of 2 unrelated malignant clones, indicating that these cases corresponded to true biclonal B-CLPD^{ref1, ref2, ref3, ref4, ref5, ref6}. Nevertheless, until now the incidence of biclonality among B-CLPD has not been established. The first goal of the present study was to determine this incidence; for that purpose, we have analyzed at diagnosis a large series of 477 consecutive patients suffering from leukemic BCLPD. Our results show that the presence of cases with 2 or more B-cell clones is a relatively frequent finding (4.8%) in B-CLPD patients. The presence of 2 or more B-cell clones was suspected by immunophenotyping and confirmed by molecular analysis of both unfractioned samples and purified B-cell populations. Accordingly, all tested samples with 2 phenotypically different B-cell subsets had 3 or more Ig gene rearrangements, and these were different in each of the B-cell populations identified; in contrast, none of the randomly selected cases with uniform phenotype had more than 2 IgH gene rearrangements. Altogether, these results suggest the utility of the immunophenotypic criteria to detect the presence of 2 or more B-cell clones. In line with previous observations^{ref1, ref2, ref3}, in most of these patients (66%) the presence of 2 or more B-cell clones was suspected based on the expression of a different sIg light chain isotype by each of the different neoplastic B-cell clones. Interestingly, in some of these cases an sIgk⁺/sIgl⁺ B-cell ratio within the normal range was observed. Despite this, in these latter cases, a detailed analysis of the immunophenotype of both the sIgk⁺ and sIgl⁺ B cells for the remaining surface markers tested revealed that both B-cell subsets were immunophenotypically aberrant^ref. These results support the notion that the analysis of the sIgk⁺/sIgl⁺ ratio by itself may not be a useful marker to detect clonality in these patients; in contrast, its combination with the identification of aberrant marker expression would be a useful sensitive and specific tool for the diagnosis of leukemic B-CLPD with 2 or more B-cell clones. The combined use of both sIg light chain together with the detection of phenotypic aberrations is also crucial for the identification of B-CLPD with 2 or more B-cell clones in which the neoplastic B-cell subsets display the same sIg light chain isotype. Accordingly, in 16 cases that showed 2 different neoplastic B-cell subpopulations with an identical sIg light chain isotype by phenotype, the existence of 2 populations that express the same sIg light chain isotype but at different intensities was frequently observed in the context of distinct aberrant phenotypes for each clone. Previous case reports on biclonal CLPD have suggested the existence of large phenotypic differences between the 2 expanded cell clones^{ref1, ref2, ref3}. In the present study, a detailed analysis of the phenotypic differences between the coexisting neoplastic cell clones showed that they are relatively variable from one diagnostic subgroup to another, and cases existed in which the phenotypic differences between clones were restricted to a single marker, together with patients displaying more complex phenotypic patterns. Virtually all antigens analyzed were found to be differentially expressed in the 2 coexisting B-cell clones. However, the incidence at which each marker displays a different reactivity in the coexisting B-cell populations varies among the different diagnostic groups. sIg was the individual marker most frequently found to be differentially expressed in the 2 B-cell clones in all diagnostic categories, this i