Focal follicular features in tonsillar diffuse large B-cell lymphomas: follicular lymphoma with diffuse areas or follicular colonization

Focal follicular features in diffuse large B-cell lymphomas (DLBCLs) are bound to raise the question of follicular lymphoma (FL) with diffuse areas, because the diagnosis of FL is based on the presence of follicular areas, even though focal. We report 7 cases of primary tonsillar DLBCLs with focal follicular features that presented with morphologic, immunohistochemical, and biological features distinct from those of FL. Histologically, these tumors were characterized by involvement of pericryptal follicles with adjacent dominant diffuse areas. Monomorphous large tumor cells were evenly spaced with abundant, often clear cytoplasm, and blastoid nuclei often with a delicate nuclear membrane. Importantly, residual germinal centers (GCs) were present in the form of either an intrafollicular GC remnant or an isolated GC in the midst of diffuse tumor. An extrafollicular and/or parafollicular growth pattern was also observed. Bcl-6 staining revealed a predominantly sporadic occurrence of Bcl-6(+) cells, comprising <50% of tumor cells, and none displayed diffusely dense collections (>75%) of Bcl-6(+) tumor cells characteristic of the GC or FL. Staining for CD10 was negative in 6 cases. Five of 7 patients were younger than 60, the median age of other patients with primary tonsillar DLBCL. No extratonsillar involvement was seen at 18 months after diagnosis. After chemotherapy or radiotherapy, complete remission was achieved with ease in all patients, but 2 patients who were treated with chemotherapy alone relapsed at 24 and 30 months. In conclusion, tonsillar DLBCL includes a small (10%) but distinct subgroup that warrants distinction from FL with predominant diffuse areas or de novo DLBCL. It appears that the focal follicular features in tonsillar DLBCL likely represent follicular colonization of marginal zone B-cell lymphoma, probably high-grade, if the possibility of FL is excluded.     

CD5-positive diffuse large B cell lymphoma arising from a CD5-positive follicular lymphoma

Follicular lymphoma (FL) is a neoplasm originating from germinal centre cells, corresponding to 25-40% of non-Hodgkin's lymphomas. Transformation into diffuse large B cell lymphoma (DLBCL) occurs in about one-third of cases. CD5 is expressed in B-chronic lymphoid leukaemia/small lymphocytic lymphoma and mantle cell lymphoma, but can rarely be expressed in conjunction with CD10 in well-documented cases of FL. In this report one case of grade 1 FL is described, which transformed into a DLBCL 6 months after initial diagnosis, with both tumours expressing CD5. In both specimens, neoplastic cells were strongly positive for CD20, CD79a, bcl-2, bcl-6 and CD5 in virtually all cells. CD10 was strongly positive in initial specimens and weakly positive in the DLBCL. Investigation using the PCR confirmed the derivation of the DLBCL from the FL as they presented the same immunoglobulin heavy chain gene rearrangement and the same BCL2-J(H) break point.     

Sequential development of diffuse large B-cell lymphoma in a patient with angioimmunoblastic T-cell lymphoma

Lymphoma of different histologic type can occur in the same patient. Here, we describe a 64-year-old male patient with angioimmunoblastic T-cell lymphoma (AITL) who subsequently developed diffuse large B-cell lymphoma (DLBCL). At the time of initial diagnosis, histologic examination of a left inguinal lymph node of the patient and a monoclonal pattern of TCRβ gene rearrangement showed typical features of AITL, and there was no evidence of a monoclonal B-cell population. Twenty-six months later, he had generalized lymphadenopathy and organs involvement by DLBCL. A monoclonal IgH gene rearrangement proved de novo development of secondary B-cell lymphoma and excluded relapse of a primary composite lymphoma. The in situ hybridization analysis showed Epstein-Barr-encoded RNA (EBER) sporadic positivity in sample collected from AITL but extensive positivity in the immunoblasts collected from DLBCL. Our observation supports the hypothesis that Epstein-Barr virus (EBV) is etiologically related to AITL in this case. Clonal expansion of EBV-associated DLBCL is a secondary event in AITL via EBV infection or reactivation.     

A case of composite classical and nodular lymphocyte predominant Hodgkin lymphoma with progression to diffuse large B‐cell non‐Hodgkin lymphoma: Diagnostic difficulty in fine‐needle aspiration cytology

A small percentage of nodular lymphocytic predominant Hodgkin lymphoma (NLPHL) progresses to diffuse large B‐cell lymphoma (DLBCL). There have also been rare reports of gray zone lymphoma with features intermediate between classical Hodgkin lymphoma (CHL) and DLBCL. We report a very rare case of composite lymphoma (CHL and NLPHL) progressing to DLBCL, and highlight the diagnostic difficulty faced during its fine‐needle aspiration (FNA) cytology diagnosis. A 65‐year‐old woman presented with a right axillary swelling which was subjected to FNA cytology. The routine FNA cytology diagnosis was anaplastic large cell lymphoma (ALCL) but immunocytochemistry did not support this diagnosis completely. The histopathological diagnosis of the excised lymph node was NLPHL with progression to DLBCL in our hospital but in a hospital abroad where the patient was treated, the reviewed diagnosis was CHL. The patient had a rapid downhill course with development of terminal pleural effusion and died approximately one year from initial diagnosis.The review of the cyto‐histologic material along with additional immunocyto/histochemical studies and the clinical course of the disease support the diagnosis of a composite lymphoma (CHL and NLPHL) with progression to DLBCL. It is suggested that all the three lesions were clonally related. Diagn. Cytopathol. 2017;45:262–266. © 2016 Wiley Periodicals, Inc.     

Primary central nervous system B cell lymphoma with features intermediate between diffuse large B cell lymphoma and Burkitt lymphoma

B cell lymphoma with features intermediate between diffuse large B cell lymphoma and Burkitt lymphoma (DLBCL/BL) is a new lymphoma entity which is recognized in the current World Health Organization (WHO) classification (2008). We report a case of a primary central nervous system lymphoma (PCNSL) with findings consistent with DLBCL/BL. It is characterized by a very aggressive clinical course, and a widespread multifocal involvement of the CNS. Our case shows that a DLBCL/BL can manifest in the CNS alone without any systemic involvement.     

Expression of multidrug resistance 1 gene in B‐cell lymphomas: association with follicular dendritic cells

Aims: Multidrug resistance (MDR) in B‐cell lymphomas still constitutes a major obstacle to the effectiveness of chemotherapy even in the anti‐CD20 antibody therapy era. The aim of this study was to investigate the expression of MDR‐associated molecules in reactive lymphadenopathy (RL), follicular lymphoma (FL), and diffuse large B‐cell lymphoma (DLBCL). Methods and results: The expression of mRNA for ABC‐transporter family genes was determined by real‐time RT‐PCR in lymph nodes from RL, FL, and DLBCL cases. MDR1 exhibited significantly stronger expression in RL, FL, and DLBCL than Raji B‐cell lymphoma cells. RL and FL showed significantly higher expression than DLBCL. Immunohistochemically, MDR1 positive cells were localized in the germinal centers of RL and center of the nodular lesions of FL showing associations with CD21 positive follicular dendritic cells (FDCs). Raji cells were co‐cultured with FDC sarcoma‐derived cells and the expression of MDR1 and drug resistance were analyzed. The co‐culture of Raji cells with FDCs induced strong expression of MDR1 and introduced resistance to doxorubicin‐induced apoptosis. Conclusions: These results suggest that FDCs induce MDR1 expression in reactive as well as neoplastic B‐cells. Inhibition of the interaction of FDCs with B‐cells may provide a novel strategy for treating the chemotherapy resistant fraction.     

B cell lymphoma,unclassifiable, with features intermediate between diffuse large B cell lymphoma and classical hodgkin lymphoma: Diagnosis by fine‐needle aspiration cytology

A 58‐year‐old lady presented with mediastinal lymphadenopathy. A thoracoscopic ultrasound‐guided fine‐needle aspiration showed large atypical epithelioid cells arranged in cohesive sheets and dispersed as single cells with intact cytoplasm amid a background of lymphocytes and histiocytes. A cytological diagnosis of “a malignant neoplasm” was made, raising a broad list of differential diagnoses. A broad panel of immunocytochemical stains performed on the cell block was indicative of a lymphoproliferative disorder, but the immunophenotype was intermediate between diffuse large B cell lymphoma (DLBCL) and classical Hodgkin lymphoma (cHL). Diffuse and strong reactivity to CD20, CD79a, and PAX‐5, and weak reactivity to CD30, was in favor of a DLBCL, or more precisely mediastinal (thymic) large B cell lymphoma (MLBL). However, there were negative staining for LCA, OCT‐2, and BOB‐1 as well as positive staining for EBV‐encoded RNA, which were against a diagnosis of MLBL and raised the possibility of cHL. The absence of RS cells and the typical mileu, the negativity for CD15 and the strong positivity of CD20 and PAX‐5 were against a diagnosis of cHL. On this basis, the diagnosis of “B‐cell lymphoproliferative disorder with features intermediate between DLBCL and cHL” was rendered. The diagnosis was subsequently confirmed on excisional biopsy. This case report demonstrates broad differential diagnoses raised by this diagnostic entity and the importance of an adequate cell block for accurate designation. Diagn. Cytopathol. 2014;42:690–693. © 2013 Wiley Periodicals, Inc.     

The t(14;18)(q32;q21) with extra MYC signal - is it a gray zone lymphoma?

Double-hit lymphomas (DHL) are defined as B-cell lymphoma with a chromosomal breakpoint affecting the MYC/8q24 locus in combination with rearrangement at (14;18)(q32;q21). We recently observed three cases of B-cell lymphoma with an extra intact MYC signal in association with the t(14;18)(q32;q21) translocation. The impact of an extra copy of MYC to the clinical course and prognosis of one patient with Diffuse Large B Cell Lymphoma (DLBCL) and two patients with Follicular Lymphoma (FL) was evaluated. Flow cytometry in all cases demonstrated lambda- or kappa-light chain restricted CD20 and CD10 positive neoplastic B cells. FISH analysis was negative for MYC gene rearrangement but demonstrated an extra copy of intact MYC. Tissue sections displayed typical starry sky “gray zone” lymphoma morphology in case of DLBCL and FL morphology in cases 2 and 3, with high Ki67 labeling in all three cases. All patients responded well to initial chemotherapy although displayed variant outcome after initial remission. The patient with DLBCL deceased within a year of diagnosis while the other two patients with FL showed much better overall survival. Our limited experience showed that additional copy of intact MYC may be equivalent to “classic” DHL on the background of DLBCL with additional cytogenetic abnormalities, however isolated t(14;18)(q32;q21) translocation in combination with additional copy of intact MYC may demonstrate histology and clinical outcome more comparable with “classic” low grade follicular lymphoma, albeit with more aggressive morphology.     

Development of angioimmunoblastic T-cell lymphoma after treatment of diffuse large B-cell lymphoma: a case report and review of literature

Cases of diffuse large B-cell lymphoma (DLBCL) arising after the initial diagnosis of angioimmunoblastic T-cell lymphoma (AITL) and DLBCL synchronous with AITL have been reported. To date, there is no report on the subsequent development of AITL in patients with DLBCL. Here we presented a rare case of AITL developing six months after the initial diagnosis of DLBCL. In order to investigate the clinical and molecular features of patients with AITL and DLBCL, we also reviewed the literature on AITL patients developing DLBCL, and patients with composite AITL and DLBCL.     

Primary pancreatic diffuse large B‐cell lymphoma diagnosed by endoscopic ultrasound guided FNAC: A rare entity

Primary pancreatic lymphoma (PPL) is an uncommon neoplasm which can clinico‐radiologically mimic carcinoma. But the management of these patients differs from that of a carcinoma. Endoscopic ultrasound (EUS) guided fine‐needle aspiration (FNA) serves as a potential tool to identify pancreatic lymphomas and thus prevent an invasive diagnostic test. This case report describes the presentation and diagnosis of primary pancreatic lymphoma. A 37‐year‐old female presented with nausea, vomiting with signs of icterus and elevated liver function test and Bilirubin. Abdominal computed tomography (CT) revealed a hypodense lesion in the head of the pancreas. EUS guided FNA was performed and cytological material was collected. The lesion was diagnosed as Non‐Hodgkin Lymphoma (NHL) and subtyped as diffuse large B‐cell lymphoma‐germinal centre (DLBCL‐GCB) base on immunohistochemistry on cell block. The patient was started on rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone (RCHOP) regimen. EUS guided FNA along with ROSE, cell bock, and immunocytochemistry helps in the diagnosis of primary pancreatic lymphoma.     

Efficacy of rituximab plus chemotherapy in follicular lymphoma depends on Ki-67 expression

Rituximab is widely used for the treatment of B-cell non-Hodgkin's lymphoma (NHL), and encouraging results have been obtained. However, some CD20-positive NHL show minimal response to rituximab, indicating that the treatment effect depends on the presence or absence of an unidentified factor. We analyzed the relationship between the effect of rituximab plus chemotherapy and expression of Ki-67, p53 and bcl-2 and several clinical variables in cases of B-NHL, particularly follicular lymphoma (FL) and diffuse large B-cell lymphoma (DLBCL). Forty-four patients were included in the present study, and the overall treatment response rate was 68%. Twelve of 30 patients (40%) achieved a complete response, five (16%) reached an unconfirmed complete response and 13 (43%) achieved a partial response. A high serum lactate dehydrogenase level and International Prognostic Index of high or high intermediate risk were associated with a decreased response in the case of FL. Immunohistochemical assays were performed in 18 FL patients (55%) and 15 DLBCL patients (45%). Significant correlation was found between an inferior response to treatment and high Ki-67 expression in the cases of FL (P = 0.006). p53 and bcl-2 expression did not correlate significantly with the response rate. The cell cycle appears to be an important factor in the efficacy of rituximab treatment. Ki-67 expression might be a predictor of efficacy of rituximab plus chemotherapy.     

Lymphocyte predominant Hodgkin lymphoma,antigen‐driven after all?

Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) was suggested as an entity separate from other types of Hodgkin lymphoma 40 years ago and recognized in the WHO classification in 2001. Based on its relatively benign course with late distant relapses, relation with lymph node hyperplasia with progressively transformed germinal centers, presence of clonal immunoglobulin gene rearrangements with somatic hypermutations and ongoing mutations, and relation with a number of inherited defects affecting the immune system, it has been suspected that NLPHL might be antigen‐driven. Recent evidence has shown that cases of IgD‐positive NLPHL are associated with infection by Moraxella catarrhalis, a common bacterium in the upper respiratory tract and in lymph nodes. This review summarizes the evidence for NLPHL as a B‐cell lymphoma involving follicular T‐lymphocytes normally found in germinal centers, its molecular features and relation to inherited immune defects, and its relation and differential diagnosis from similar entities. Finally, it discusses the evidence that in many cases a watch and wait policy might be a viable initial management strategy. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Diffuse large B-cell lymphoma arising in a composite lymphoma with biclonality by flow cytometry and one monoclonal band by PCR

Composite lymphoma (CL) refers to the presence of two or more distinct types of lymphomas in a single organ or tissue. CL is an infrequent finding and may be due to the existence of two genetically related neoplasms, i.e. transformation of a single lymphoma into another lymphoma, or be due to the presence of two clonally unrelated lymphomas. CL composed of more than two lymphomas is even rare. Herein we describe a case of diffuse large B-cell lymphoma (DLBCL) arising in a CL of follicular lymphoma (FL) and small lymphocytic lymphoma (SLL) in an inguinal lymph node of an 85 year old woman. The three lymphomas were morphologically and immunophenotypically distinct while flow cytometry detected two monoclonal B-cell populations. Karyotyping and Polymerase Chain Reaction (PCR) for B-cell clonality each detected a single monoclonal B-cell population. The morphology findings may suggest DLBCL being transformed from FL while Richter transformation from SLL appears to be less likely in our case. Due to the single clone by chromosome study and PCR study, the precise relationships of the three lymphomas are unknown.     

Large-cell transformation of a composite lymphoma

Composite lymphoma is a rarely reported entity, defined as two or more morphologically distinct types of lymphoma at the same anatomic site, occurring either synchronously or metachronously. Since 1978, about 100 case reports of composite lymphoma have been cited, many involving combinations of low-grade B-cell lymphomas. To our knowledge, no cases of large-cell transformation of composite lymphoma have yet been described. We report the case of a patient who presented with diffuse large B-cell lymphoma (DLBCL) fifteen years after successful treatment for a mature B-cell lymphoma. Reassessment of the patient's lymph node from 1995, using techniques not previously available, resulted in a revised diagnosis of composite lymphoma, comprising both follicular lymphoma (FL) and small lymphocytic lymphoma (SLL). Analysis of B-cell gene rearrangement studies using BIOMED-2-based PCR, and of t(14;18) rearrangements by both FISH and PCR, provided evidence that the DLBCL evolved from transformation of the composite lymphoma, specifically from its FL component. B-cell gene rearrangement studies also supported a clonal relationship between the FL and SLL components of the composite lymphoma.     

T-lymphoblastic lymphoma arising in the small intestine.

The authors report the clinical, pathological and immunological features of a case of T-lymphoblastic lymphoma presenting with protein-losing enteropathy. There was extensive multifocal involvement of the duodenum, jejunum and ileum. The mediastinum was not enlarged; the peripheral blood picture and bilateral bone marrow trephine biopsies were unremarkable. The tumor cells were positive for terminal deoxynucleotide transferase, CD3, CD2, CD7 and CD10; they were negative for CD1, CD5, CD4, CD8 and HLA-DR. The immunophenotype was that of an immature thymic T-cell. Monocytic and B-cell markers were negative. Despite initial dose reduction in chemotherapy, the patient still developed massive intestinal hemorrhage and succumbed 2 wks after treatment. Postmortem examination confirmed absence of thymic involvement. The overall picture strongly suggests a primary intestinal origin of this T-lymphoblastic lymphoma which contradicts the conventional wisdom that T-lymphoblastic lymphoma arises in the thymus from primitive cortical lymphocytes before rapidly disseminating.     

Epstein–Barr virus‐positive diffuse large B cell lymphoma arising from a chronic lymphocytic leukemia: Overlapping features with classical Hodgkin lymphoma

A small proportion of patients with chronic lymphocytic leukemia (CLL) may progress to large cell lymphoma, or Richter syndrome (RS). The large cells of RS may arise through transformation of the original CLL clone (clonally related) or represent a new neoplasm (clonally unrelated), which might be Epstein–Barr virus (EBV)‐associated. We present a 61‐year‐old male with 5‐year history of CLL who developed RS on bilateral adrenal glands. The tumor showed a vague nodular growth pattern separated by thick fibrous bands and the tumor cells were large and pleomorphic, with focal sheet‐like growth pattern, in a background of small B and T‐lymphocytes. The large tumor cells were positive for CD15, CD19, CD20 (intensely and diffusely), CD30, fascin, PAX5, MUM1, OCT2, and LMP‐1 by immunohistochemical stains, and EBV by in situ hybridization. The tumor was diagnosed as EBV‐positive diffuse large B cell lymphoma (DLBCL), with overlapping features of classic Hodgkin lymphoma (CHL). The patient received salvage chemotherapy and was free of disease 2 years after adrenalectomy. We speculated that our case was a clonally unrelated tumor with his underlying CLL and discussed the differential diagnoses between EBV‐positive DLBCL and CHL in the setting of RS.     

Nodular lymphocyte predominant Hodgkin lymphoma and diffuse large B-cell lymphoma: a study of six cases concurrently involving the same site

Cotta C V, Coleman J F, Li S & Hsi E D
(2011) Histopathology  59 , 1194–1203
Nodular lymphocyte predominant Hodgkin lymphoma and diffuse large B‐cell lymphoma: a study of six cases concurrently involving the same site Aims: Nodular lymphocyte‐predominant Hodgkin lymphoma (NLPHL) is a slowly progressing neoplasm with a favourable prognosis. However, in a minority of cases (3–12%) it progresses to a clonally related diffuse large B‐cell lymphoma (DLBCL), diagnosed between 6 months and 24 years after NLPHL. This study investigated six cases of NLPHL and DLBCL at the same location. Methods and results: The patients were five men and one woman. In four cases, the site was an axillary lymph node, and in two it was inguinal. In all cases, NLPHL areas had typical morphological and immunophenotypic features. DLBCL involvement was multifocal, diffuse, and characterized by large centroblastic and anaplastic cells. Immunohistochemical studies showed DLBCL cells to be positive for CD20, CD45, and BCL6. In one case, DLBCL cells were positive for BCL2, and in two cases they were positive for MUM‐1. There were no networks of follicular dendritic cells (FDC) associated with DLBCL. Rosettes of PD‐1‐positive and CD57‐positive cells surrounding malignant cells in NLPHL were absent in DLBCL. All the cases were negative for Epstein–Barr virus. No translocations involving MYC were identified in DLBCL. Treatment and outcome were known in four cases. All of these patients were treated with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R‐CHOP), and this was followed by clinical remission (CR). Conclusions: In adequately sampled tumors, DLBCL can be associated with NLPHL at diagnosis. Diffuse architecture, loss of FDC networks, sometimes immunophenotype shift are characteristics of DLBCL associated with NLPHL. Treatment with R‐CHOP usually leads to CR.     

Amplification of 2p as a genomic marker for transformation in lymphoma

To outline further genetic mechanisms of transformation from follicular lymphoma (FL) to diffuse large B‐cell lymphoma (DLBCL), we have performed whole genome array‐CGH in 81 tumors from 60 patients [29 de novo DLBCL (dnDLBCL), 31 transformed DLBCL (tDLBCL), and 21 antecedent FL]. In 15 patients, paired tumor samples (primary FL and a subsequent tDLBCL) were available, among which three possessed more than two subsequent tumors, allowing us to follow specific genetic alterations acquired before, during, and after the transformation. Gain of 2p15–16.1 encompassing, among others, the REL, BCL11A, USP34, COMMD1, and OTX1 genes was found to be more common in the tDLBCL compared with dnDLBCL (P < 0.001). Furthermore, a high‐level amplification of 2p15–16.1 was also detected in the FL stage prior to transformation, indicating its importance during the transformation event. Quantitative real‐time PCR showed a higher level of amplification of REL, USP34, and COMMD1 (all involved in the NFκΒ‐pathway) compared with BCL11A, which indicates that the altered genes disrupting the NFκΒ pathway may be the driver genes of transformation rather than the previously suggested BCL11A. Moreover, a 17q21.33 amplification was exclusively found in tDLBCL, never in FL (P < 0.04) or dnDLBCL, indicating an upregulation of genes of importance during the later phase of transformation. Taken together, our study demonstrates potential genomic markers for disease progression to clinically more aggressive forms. We also confirm the importance of the TP53‐, CDKN2A‐, and NFκΒ‐pathways for the transformation from FL to DLBCL. © 2014 Wiley Periodicals, Inc.     

Secondary parenchymal CNS involvement by lymphoma including rare types: Follicular and EBV-positive NK/T cell lymphoma,nasal type

BackgroundSecondary CNS involvement by systemic lymphomas (SCNSL) is uncommon, but when it occurs, is usually due to diffuse large B cell lymphoma (DLBCL). Three recent unusual cases serve to highlight diagnostic challenges.ObjectiveTo report SCNSL from DLBCL and two unusual lymphoma types: follicular lymphoma with high-grade transformation to DLBCL and NK/T cell lymphoma, nasal type (ENKL), nasal type.ResultsSCNSL in the DLBCL case occurred at 7-year interval from primary in a 54-year-old woman who presented with stroke-like symptoms and a right postcentral gyrus 2.6 × 2.9 × 2.6 cm. mass. The follicular lymphoma occurred at 6-month interval in a 69-year-old woman with 1 month of diplopia and 2 weeks of cognitive decline; multifocal lesions involved temporal lobe, subependymal periventricular areas, brainstem, cerebellum, hypothalamus, corpus callosum and gyrus rectus. The ENKL occurred at 25-month interval from nasal biopsy in a 45-year-old man with 1 week of altered mental status; multifocal cerebral and brainstem lesions were identified. Histological features in cases 1 and 3 were identical to the primary lymphoma, with high-grade transformation to DLBCL in the follicular lymphoma.ConclusionUnusual features in our series include longer interval from primary to relapse in case 1 with DLBCL (usually <2 years of diagnosis), and SCNSL occurring from either follicular lymphoma or EKNL, nasal type (<6% of cases). Pathologists play an important role in excluding infectious, especially in cases with parenchymal lesions and characterizing the lymphoma type in SCNSL.     

Gene expression profile of serial samples of transformed B-cell lymphomas

Follicular lymphoma (FL) is characterized by a continuous rate of relapse and transformation to a high-grade lymphoma, usually diffuse large B-cell lymphoma (DLBCL), associated with a dismal prognosis and a poor response to conventional chemotherapy. The progression of indolent to aggressive FL is accompanied by the successive accumulation of recurrent chromosomal defects, but the resultant alterations of gene expression are largely unknown. To expand the understanding of the pathogenesis of FL transformation, we initially performed oligonucleotide microarray analyses using Affymetrix HuFL chips on five cases with matched snap-frozen lymph nodes before and after transformation. Expression data were analyzed using the Affymetrix Microarray Suite 4.0 and Genespring 4.0. Thirty-six genes with increased expression and 66 genes with decreased expression associated with transformation were identified and functionally classified. The expression of differentially expressed genes was confirmed by real-time quantitative RT-PCR (QRT-PCR) using a total of seven matched pairs and an additional five FL and five unrelated DLBCL. In addition, selected genes were further analyzed by QRT-PCR or immunohistochemistry using a large, unrelated series of FL (grades 1 to 3) as well as transformed and de novo DLBCL (total of 51 samples). The microarray results correlated with the protein expression data obtained from samples at the time of initial diagnosis and transformation. Furthermore, the expression of 25 candidate genes was evaluated by QRT-PCR with a 78% confirmation rate. Some of the identified genes, such as nucleobindin, interferon regulatory factor 4, and tissue inhibitor of metalloproteinases 1, are already known to be associated with high-grade non-Hodgkin's lymphoma. Novel candidate genes with confirmed increased and decreased expression in transformed DLBCL include ABL2 and NEK2, and PDCD1 and VDUP1, respectively. In summary, this study shows that transformation of FL to DLBCL is associated with a distinct set of differentially expressed genes of potential functional importance.