Richter syndrome in B-cell chronic lymphocytic leukemia

Complexities in the diagnosis of large B-cell lymphomas, classic Hodgkin lymphomas and overlapping peripheral T-cell lymphomas simplified: An evidence-based guide

The diagnosis of a large B-cell lymphoma and classic Hodgkin lymphoma (CHL) is often straightforward. However, in select circumstances, these simple diagnoses can be quite complex. In part, diagnostic difficulty may be due to uncertainty in the evaluation of morphologic and immunophenotypic features along a biologic continuum, or alternatively arise from uncertainty in predicting the behavior and outcomes of patients. Here, we systematically discuss and review areas of diagnostic difficulty in the diagnosis of large B-cell lymphomas (LBCL), classic Hodgkin lymphomas (CHL) and peripheral T-cell lymphomas (PTCL). We provide careful data-driven analyses and evidence-based approaches to help guide pathologists and clinicians. We discuss: 1) marginal zone lymphomas with increased large cells versus diffuse large B-cell lymphoma (DLBCL), 2) chronic lymphocytic leukemia with expanded proliferation centers versus diffuse large B-cell lymphoma (DLBCL), 3) chronic lymphocytic leukemia with Hodgkin/Reed-Sternberg-like cells versus CHL arising from chronic lymphocytic leukemia, 4) complex cases of follicular lymphoma versus DLBCL, 5) PTCL with large B-cell proliferations versus PTCL with LBCL, 6) PTCL with Hodgkin/Reed-Sternberg-like cells versus CHL, and finally 7) blastoid/pleomorphic mantle cell lymphoma versus DLBCL. Our evidence and data driven approach may serve as a useful diagnostic guide.

Secondary B-cell lymphoma associated with the Epstein-Barr virus in chronic lymphocytic leukemia patients

Up to 10 % of chronic lymphocytic leukemia (CLL) patients present with aggressive secondary B-cell lymphoma (most frequently diffuse large B-cell lymphoma, DLBCL) which may be clonally related to the CLL (i.e., Richter transformation, RT, 80 % of the cases) or de novo (20 % of the cases). Several genetic lesions associated with RT have already been identified, but the potential role of the Epstein-Barr virus (EBV) has been largely overlooked. In this study, we describe six CLL patients who developed a secondary EBV-positive (EBV⁺) B-cell lymphoma (five DLBCL, one Hodgkin lymphoma) and compare their clinicopathological characteristics to ten CLL patients with EBV-negative (EBV^-) secondary B-cell lymphomas (all DLBCL). All 16 patients had a history of iatrogenic immunosuppression or chemotherapy. Eighty percent had received fludarabine as part of the CLL treatment. Most secondary lymphomas were clonally related to the previous CLL (3/4 EBV⁺, 7/7 EBV^- cases tested). Notably EBV⁺ RT was associated with a trend for older age at onset (median 72 vs. 63 years, p value >0.05), longer interval between CLL and RT diagnosis (median 4.2 vs. 2.9 years, p value >0.05), and shorter overall survival (median 4 vs. 10 months, p value >0.05). These differences were not significant, probably due to small sample size. Immunohistochemical profiling suggested more frequent overexpression of TP53 and MYC in EBV^- compared to EBV⁺ secondary lymphoma. Based on this small retrospective single center series, we hypothesize that EBV⁺ RT may constitute a separate subgroup of RT. Larger series are required to validate this suggestion.

Hodgkin lymphoma variant of Richter transformation: morphology, Epstein-Barr virus status, clonality, and survival analysis-with comparison to Hodgkin-like lesion

Hodgkin/Reed-Sternberg (HRS) cells in the setting of chronic lymphocytic leukemia (CLL) exist in 2 forms: type I with isolated HRS cells in a CLL background (Hodgkin-like lesion) and type II with typical classic Hodgkin lymphoma, a variant of Richter transformation (CHL-RT). The clinical significance of the 2 morphological patterns is unclear, and their biological features have not been compared. We retrospectively reviewed 77 cases: 26 of type I and 51 of type II CHL-RT; 3 cases progressed from type I to type II. We examined clinical features, Epstein-Barr virus (EBV) status, and clonal relatedness after microdissection. Median age for type I was 62 years versus 73 years for type II (P=.01); 27% (type I) versus 73% (type II) had a history of CLL. HRS cells were positive for EBV in 71% (55/77), similar in types I and II. Clonality analysis was performed in 33 cases (type I and type II combined): HRS cells were clonally related to the underlying CLL in 14 and unrelated in 19. ZAP-70 expression of the CLL cells but not EBV status or morphological pattern was correlated with clonal relatedness: all 14 clonally related cases were ZAP-70 negative, whereas 74% (14/19) of clonally unrelated cases were ZAP-70 positive. Overall median survival (types I and II) after diagnosis was 44 months. Advanced age was an adverse risk factor for survival, but not histologic pattern, type I versus type II. HRS-like cells in a background of CLL carries a similar clinical risk to that of CHL-RT and may progress to classic Hodgkin lymphoma in some cases.

CD5- and CD23-positive splenic diffuse large B-cell lymphoma with very low CD20 expression

We report a rare primary splenic diffuse large B-cell lymphoma demonstrating CD5(+) and CD23(+) with very low CD20 expression. The only lesion was detected in the spleen, which was extremely enlarged with multiple large white-colored nodules. The lesion was characterized by a diffuse growth pattern of medium- to large-sized lymphoma cells with abundant cytoplasm. Immunohistochemical and flow cytometric study demonstrated that the lymphoma cells were negative for CD2, CD3, CD4, CD8, CD10, CD56, CD138, ALK-1, λ-light chain, and cyclin-D1, and positive for CD5, CD19, CD23, CD25, CD38, CD43, CD79a, IgM, IgD, κ-light chain, BCL2, BCL6, BOB. 1, Oct-2, Pax5, and MUM-1. CD20 was very weakly positive immunohistochemically, and negative by flow cytometric analysis. These findings resembled Richter syndrome, although chronic lymphocytic leukemia was not preexisting. Extremely poor outcome might be supposed because the effect of rituximab might be quite limited since CD20 was very weakly positive, in addition to an inferior prognosis of both CD20(-) and CD5(+) diffuse large B-cell lymphoma. Careful management is thus necessary.

Alternate clonal dominance in richter transformation presenting as extranodal diffuse large B-cell lymphoma and synchronous classic Hodgkin lymphoma

OBJECTIVES

Richter transformation (RT) represents the rare occurrence of a secondary aggressive lymphoma in the setting of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL).

METHODS

Here we describe the peculiar case of a patient with trisomy 12+ and atypical (CD5+, CD23-) CLL/SLL who developed a two-step RT with complex morphologic and molecular features.

RESULTS

Molecular analysis of a CLL/SLL population detected two different immunoglobulin rearrangement patterns corresponding to a main peak and a minor peak. Transformation took place both as gastric diffuse large B-cell lymphoma and as a synchronous bone marrow classic Hodgkin lymphoma with the same immunoglobulin rearrangement pattern corresponding to the minor peak detected in CLL/SLL at diagnosis. During chemotherapy, progression occurred as axillary nodal involvement by a CD5+ high-grade lymphoma with an immunoglobulin rearrangement pattern corresponding to the main CLL peak.

CONCLUSIONS

In this case, the elaborate clinical and molecular picture may be correlated to an alternate dominance of two distinct clonal populations probably influenced by therapeutic and environmental factors.

Richter syndrome with follicular colonization of chronic lymphocytic leukemia/small lymphocytic lymphoma cells mimicking follicular lymphoma

Follicular colonization is occasionally observed in marginal zone lymphoma. In rare cases, it has also been associated with mantle cell lymphoma. Chronic lymphocytic leukemia typically involves nodal or extranodal tissues as diffuse proliferation by complete effacement of the normal architecture. The involvement of chronic lymphocytic leukemia may be less frequently limited to the interfollicular areas. Here, we report a case of Richter syndrome of the small intestine that was initially diagnosed as follicular lymphoma of the gastrointestinal tract because of a partial follicular growth pattern in addition to a mainly diffuse proliferation pattern. The follicular pattern mimicking follicular lymphoma was shown to be composed of reactive follicles with follicular colonization of the original chronic lymphocytic leukemia cells. As the prognoses of Richter syndrome and follicular lymphoma of gastrointestinal tract are quite different, clinicians must carefully diagnose these conditions to avoid a misdiagnosis.

Development of diffuse large B-cell lymphoma in a patient with Waldenström's macroglobulinemia/lymphoplasmacytic lymphoma: clonal identity between two B-cell neoplasms

Waldenström's macroglobulinemia (WM)/ lymphoplasmacytic lymphoma (LPL) is an indolent mature B-cell neoplasm. In rare cases of WM/LPL, diffuse large B-cell lymphoma (DLBCL) develops as a result of histologic transformation. In this report, we present a case of DLBCL developing in a patient with WM/LPL. Combination chemotherapy for DLBCL was effective and complete remission was eventually achieved. We attempted to determine the clonal relatedness between WM/LPL and DLBCL in the patient by analyzing complementarity-determining region 3 (CDR3) in the immunoglobulin heavy chain gene. A common CDR3 sequence was found in tumor cells of DLBCL and those of WM/LPL, indicating that tumor cells of DLBCL are clonally identical to those of WM/LPL. Therefore, in the present case, DLBCL is developed from WM/LPL cells by clonal evolution.

Development of diffuse large B-cell lymphoma in a patient with Waldenström's macroglobulinemia/lymphoplasmacytic lymphoma: clonal identity between two B-cell neoplasms

Waldenström's macroglobulinemia (WM)/ lymphoplasmacytic lymphoma (LPL) is an indolent mature B-cell neoplasm. In rare cases of WM/LPL, diffuse large B-cell lymphoma (DLBCL) develops as a result of histologic transformation. In this report, we present a case of DLBCL developing in a patient with WM/LPL. Combination chemotherapy for DLBCL was effective and complete remission was eventually achieved. We attempted to determine the clonal relatedness between WM/LPL and DLBCL in the patient by analyzing complementarity-determining region 3 (CDR3) in the immunoglobulin heavy chain gene. A common CDR3 sequence was found in tumor cells of DLBCL and those of WM/LPL, indicating that tumor cells of DLBCL are clonally identical to those of WM/LPL. Therefore, in the present case, DLBCL is developed from WM/LPL cells by clonal evolution.

Genomic profiling of Richter's syndrome: recurrent lesions and differences with de novo diffuse large B-cell lymphomas

Richter's syndrome (RS) represents the transformation of chronic lymphocytic leukaemia (CLL) to aggressive lymphoma and is mostly represented by diffuse large B-cell lymphoma (DLBCL), with a post-germinal centre (GC) phenotype, clonally related to the pre-existing CLL. RS has a very poor prognosis and its pathogenetic mechanisms are poorly understood. In order to gain additional hints in RS pathogenesis, we performed a genome-wide DNA profiling study of 13 RS phases and eight matched CLL phases using the Affymetrix Human Mapping 250K NspI SNP arrays. Individual genomic profiles were heterogeneous, with no individual lesions occurring in more than half of the cases. However, several observations suggest that MYC pathway might be involved in RS. The 13q13.3-qter region containing MIRHG1 (MIR-17-92), a cluster of microRNA interacting with c-MYC, was acquired at the time of transformation. The 13q gain was coupled with the gain of c-MYC and loss of TP53. Translocation of c-MYC was acquired at transformation in a fraction of cases and this event appeared mutually exclusive with gain of MIRHG1. MYCN, a c-MYC homologue, was also recurrently gained. By comparing RS with 48 de novo DLBCL, RS presented a significantly lower prevalence of deletions affecting the PRDM1 and TNFAIP3, genes on 6q, known to be associated with a post-GC phenotype. In conclusion, the genomic profile of RS seems to differ from what observed in de novo DLBCL and in other transformed DLBCL. Genomic lesions occurring in RS are heterogeneous suggesting the existence of different RS subsets, possibly due to different transforming mechanisms. A deregulation of MYC pathway might represent one of the main transformation events in the pathogenesis of a subset of RS clonally related to the previous CLL.

The leukemias of mature lymphocytes

The leukemias of mature B cells and T cells are a limited set of diseases in which blood and bone marrow are the primary sites of involvement. Although they may superficially resemble one another, they have distinct clinical and pathologic features and must be distinguished from one another. In this article, the major clinical, morphologic, phenotypic, and molecular genetic features of the mature B- and T-cell leukemias are reviewed, and differential diagnostic considerations are discussed.

Second neoplasms in chronic lymphocytic leukemia: incidence and pathogenesis with emphasis on the role of different therapies

Several surveys have defined chronic lymphocytic leukemia (CLL) patients as a high-risk patient population for developing second neoplasms. As possible mechanisms underlying the increased risk of specific second malignancies in CLL patients the immunodeficiency associated with disease is generally proposed. As far as secondary acute leukemia is concerned, greater insight into the molecular pathogenesis of therapy-related acute myeloid leukemia (AML) developing in CLL would allow to avoid treatment regimens that can lead to this complication. Richter's syndrome continues to be a fatal and highly refractory to chemotherapy disease complicating the clinical course of CLL. Therefore, experimental approaches of therapy should be considered in its treatment. Given the prolonged survival of patients with CLL, it is important to recognize early a second cancer especially whether new symptoms or physical findings arise.

ALK-Positive Anaplastic Large Cell Lymphoma in a Patient With Chronic Lymphocytic Leukemia

This article reports the case of a 59-year-old patient with an 8-year history of chronic lymphocytic leukemia (CLL), prostate carcinoma, and squamous cell carcinoma who developed an ALK-positive anaplastic large cell lymphoma (ALCL). Lymph node and bone marrow biopsies showed 2 distinct morphologic populations: ( a) the CLL component showing a diffuse monomorphous infiltrate of small lymphocytes with the typical immunophenotype showing positive CD20, CD5, CD23, and κ light chain restriction and ( b) the ALCL component showing large anaplastic pleomorphic cells positive for CD30, CD45, ALK, CD45Ro, CD4, and vimentin. Polymerase chain reaction performed on the lymph node for immunoglobulin heavy chain and T-cell receptor γ and β showed gene rearrangements after macrodissection of morphologically distinct populations, indicating confirmed genetically distinct populations. Despite intensive chemotherapy, the patient died. This case represents the rare occurrence of an ALK-positive ALCL developing in a patient with CLL.

Intrinsic and treatment-related immune alterations in chronic lymphocytic leukaemia and their impact for clinical practice

BACKGROUND

Chronic lymphocytic leukaemia patients harbour important impairments in both their cellular- and humoral-mediated immunity, which accounts for their notorious susceptibility to a multitude of infections and various autoimmune cytopenias. It has also been shown that the rate of second cancers is increased in chronic lymphocytic leukaemia.

OBJECTIVE

The aim of this study was to review the immune alterations in untreated and treated chronic lymphocytic leukaemia and define their impact for clinical practice.

METHODS

The author gives a comprehensive review of the most relevant preclinical and clinical studies pertaining to various immune abnormalities and infectious complications in both untreated and treated chronic lymphocytic leukaemia. Landmark clinical trials involving the contemporary chronic lymphocytic leukaemia chemo- and immunotherapies, alone or in combination, as well as the main epidemiological studies establishing the increased rate of second cancers in chronic lymphocytic leukaemia are also discussed.

RESULTS/CONCLUSIONS

Iatrogenic immunosuppression in chronic lymphocytic leukaemia alters the pattern of opportunistic infections, can cause autoimmune cytopenias and might further increase the rate of second malignancies in patients whose disease already places them at a greater risk. Careful consideration of existing risk factors in chronic lymphocytic leukaemia could establish the optimal screening and follow-up schedule for chronic lymphocytic leukaemia patients as its therapeutics evolves.

CD38 gene polymorphism and chronic lymphocytic leukemia: a role in transformation to Richter syndrome?

CD38 rules proliferation signals in chronic lymphocytic leukemia (CLL) cells, suggesting that the molecule is not merely a prognostic marker but also a key element in the pathogenetic network underlying the disease. CD38 has a genetic polymorphism, characterized by a C>G variation in the regulatory region of intron 1. The working hypothesis is that the presence of different alleles in CLL patients marks (or accounts for) some of the clinical heterogeneity. CD38 allele distribution in 248 Italian patients overlapped with that of the controls (n = 232), suggesting that susceptibility to CLL is not influenced by CD38 genotype. Stratification of patients according to markers of unfavorable prognosis constantly resulted in a significantly higher frequency of the rare G allele. Furthermore, analysis of clinical parameters showed that G allele is independently associated with nodal/splenic involvement. The highest G allele frequency was observed in the 16 patients of the cohort that developed Richter syndrome (RS). Five-year cumulative incidence of transformation was significantly higher in G allele carriers than in CC homozygotes. Multivariate analysis on a total of 30 RS patients confirmed that the probability of transformation is strongly associated with G allele, likely representing an independent risk factor for RS development.

Risk factors for development of a second lymphoid malignancy in patients with chronic lymphocytic leukaemia

Previous studies suggested that patients with chronic lymphocytic leukaemia (CLL) are at a three- to fivefold increased risk of developing a second lymphoproliferative disorder (LPD). This observational cohort study used the Mayo Clinic CLL Database to identify factors associated with developing a second LPD. A second LPD was identified in 26 (2.7%) of 962 CLL patients during a median follow-up of 3.3 years. Diffuse large B-cell lymphoma was the most common subtype of secondary LPD (12 of 26 cases). Patients previously treated for CLL had a trend toward higher prevalence of second LPD (4%) compared with previously untreated patients (2%; P = 0.053). More strikingly, patients treated with purine nucleoside analogues (PNA) had a significantly increased risk of subsequent second LPD (5.2%) compared with patients who had not received PNA (1.9%; P = 0.008). No statistically significant association was observed between risk of second LPD and other CLL characteristics (ZAP-70, CD38, IgV(H) mutation status or cytogenetic abnormalities). In this series, prior treatments with PNA or anthracyclines were the only significant factors associated with risk of developing a second LPD in patients with CLL. Physicians should strictly adhere to established criteria to initiate treatment for CLL patients who are not participating in clinical trials.

Pathology of chronic lymphocytic leukemia: an update

Chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) is a clonal lymphoproliferative disorder characterized by proliferation of morphologically and immunophenotypically mature lymphocytes. CLL/SLL may proceed through different phases: an early phase in which tumor cells are predominantly small in size, with a low proliferation rate and prolonged cell survival, and a transformation phase with the frequent occurrence of extramedullary proliferation and an increase in large, immature cells. Although some patients with CLL have an indolent disease course and die after many years of unrelated causes, others have very rapidly disease progression and die of the disease within a few years of the diagnosis. In the past few years, considerable progress has been made in our ability to diagnose and classify CLL accurately. Through cytogenetics and molecular biology, it has been shown that CLL and variants are associated with a unique genotypic profile and that these genetic lesions often have a direct bearing on the pathogenesis and prognosis of the disease. Similarly, the development of antibodies to new biologic markers has allowed the identification of a unique immunophenotypic profile for CLL and variants. Moreover, accumulating evidence suggests that CLL cells respond to selected microenvironmental signals and that this confers a growth advantage and an extended survival to CLL cells. In this article, we will review the progress in the pathobiology of CLL and give an update on prognostic markers and tools in current pathology practice for risk stratification of CLL.

Comprehensive Management of the CLL Patient: A Holistic Approach

The current management of B-chronic lymphocytic leukemia (CLL) is no longer straightforward for the practicing hematologist. Rapid advances in diagnostic precision, methods of predicting prognosis, understanding of natural history of CLL, recognition of clinical complications, clarification of the quality of life (QOL) issues facing the CLL patient, and the exciting array of novel treatment approaches have made the care of the CLL patient more demanding. This review is focused on summarizing these advances in order to provide a framework for integrating this knowledge into routine hematologic practice.

Demonstration of Chimeric DNA of bcl-2 and Immunoglobulin Heavy Chain in Follicular Lymphoma and Subsequent Hodgkin Lymphoma from the Same Patient

We performed single cell polymerase chain reaction (PCR) amplification of the t (14 ; 18) translocation from paraffin embedded sections in a case of follicular lymphoma (FL) with subsequent development of Hodgkin lymphoma (HL). The lymphoma cells of FL were positive for CD20, CD10 and BCL-2, and negative for CD3, CD30 and CD15. Hodgkin and Reed-Sternberg (HRS) cells of HL were positive for CD20, CD30 and CD15, and negative for CD3 and CD10. EBER-1 RNA in situ hybridization failed to stain with both lymphomas. HRS cells manipulated and FL cells micro-shaved from individual neoplastic follicles were subjected to single-cell PCR. The t (14 ; 18) translocation, a chimeric DNA containing portions of the bcl-2 and the immunoglobulin heavy chain (IgH) genes, was amplified from four of 27 isolated HRS cells and two individual FL follicles. All t (14 ; 18) PCRs yielded products of the same size, and an identical nucleotide sequence including the t (14 ; 18) translocation was found in both FL and HRS samples. Thus, the data demonstrate the common clonal origin of FL cells and HRS cells in subsequent HL, and that both FL and HL were derived from germinal center B cells with the t (14 ; 18) translocation.

Comprehensive management of the CLL patient: a holistic approach

The current management of B-chronic lymphocytic leukemia (CLL) is no longer straightforward for the practicing hematologist. Rapid advances in diagnostic precision, methods of predicting prognosis, understanding of natural history of CLL, recognition of clinical complications, clarification of the quality of life (QOL) issues facing the CLL patient, and the exciting array of novel treatment approaches have made the care of the CLL patient more demanding. This review is focused on summarizing these advances in order to provide a framework for integrating this knowledge into routine hematologic practice.

EBV negative Richter's syndrome from a coexistent clone after salvage treatment with alemtuzumab in a CLL patient

Transformation of B cell chronic lymphocytic leukemia (B-CLL) to large cell lymphoma or Hodgkin's disease is known as a Richter's syndrome (RS). According to the literature, 1-10% of B-CLL patients develop this high-grade lymphoid malignancy. The relationship between the immunosuppressive effect of nucleoside analogues (NA) and monoclonal antibodies and the development of large cell transformation still remains a controversial issue. We describe a CLL patient who developed a large B cell lymphoma 94 months after diagnosis and 3 months after the start of alemtuzumab. The CLL immunophenotype was retained by the transforming cells although a different light chain was expressed. Molecular analysis of the immunoglobulin heavy chain confirmed that the CLL and the RS had a different clonal origin. Subsequent molecular analyses of stored samples showed that the clone with transforming capacity already appeared two years before the clinical appearance of the RS. We hypothesize that alemtuzumab promoted the uncontrolled growth of the latest clone by eradicating the initial B-CLL clone efficiently, and by inducing a strong T cell depletion with consequent impairment of the immunosurveillance. We also ruled out that the RS was EBV driven. In conclusion, we report a case of EBV negative RS after alemtuzumab as salvage therapy.

Second neoplasms in patients with chronic lymphocytic leukemia

Second malignancies occur with increased frequency in patients with chronic lymphocytic leukemia (CLL) regardless of treatment, but they may be more frequent and more aggressive after nucleoside analog therapy of CLL. In as many as 33% of patients with CLL who develop a second malignancy, a spontaneous remission of CLL precedes the diagnosis of the second malignancy by months or years. Richter's syndrome, whether manifested by anaplastic large cell lymphoma or Hodgkin's disease, is not truly a second malignancy because the CLL clone appears to be involved. However, all other malignancies developing in patients with CLL appear to be derived from a different clone. CLL and the second malignancy may have a common viral etiology. Second malignancies in patients with CLL should be treated as they would be in patients without CLL.

A Common Clonal Origin of Nodal Marginal Zone B-Cell Lymphoma and Plasma Cell Myeloma Demonstrating Different Immunophenotypes

We demonstrated an 83-year-old male case of composite lymphoma. Before 18 years, he was diagnosed with nodal marginal zone B-cell lymphoma in the cervical lymph node. Peripheral blood showed anemia and IgA (kappa)-type monoclonal gammopathy (IgA; 3,625 mg/dL). Bone marrow aspiration biopsy exhibited plasma cell myeloma, in which atypical plasma cells were positive for cytoplasmic IgA (kappa) and atypical lymphoid cells intermingled were positive for CD20. In contrast, cervical lymph node biopsy revealed nodal marginal zone B-cell lymphoma, in which lymphoma cells were positive for cytoplasmic IgG (lambda). Southern blotting analysis of the IgH gene showed same clonal rearrangement band in both lymph node and bone marrow samples and additional band in the bone marrow. Sequence analyses of the IgH gene showed an identical sequence of CDR3 in both samples. Thus, we demonstrated a common clonal origin of composite lymphoma comprising nodal marginal zone B-cell lymphoma and plasma cell myeloma. Nodal marginal zone B-cell lymphoma recurred in cervical lymph node and involved into the bone marrow, differentiating into plasma cell myeloma in which Ig isotype switched and monoclonal gammopathy developed. Sequence analysis of the IgH gene was a powerful tool for determination of clonal origin.