Identification of cytogenetic subgroups and karyotypic pathways of clonal evolution in follicular lymphomas

Molecular Biomarkers in Prediction of High-Grade Transformation and Outcome in Patients with Follicular Lymphoma: A Comprehensive Systemic Review

Follicular lymphoma (FL) is the most prevalent indolent B-cell lymphoma entity, often characterized by the t(14;18) BCL2-IGH translocation. The malignancy represents a clinically and biologically highly heterogeneous disease. Most patients have favorable prognoses; however, despite therapeutic advancements, the disease remains incurable, with recurrent relapses or early disease progression. Moreover, transformation to an aggressive histology, most often diffuse large-B-cell lymphoma, remains a critical event in the disease course, which is associated with poor outcomes. Understanding the individual patient's risk of transformation remains challenging, which has motivated much research on novel biomarkers within the past four decades. This review systematically assessed the research on molecular biomarkers in FL transformation and outcome. Following the PRISMA guidelines for systemic reviews, the PubMed database was searched for English articles published from January 1984 through September 2024, yielding 6769 results. The identified publications were carefully screened and reviewed, of which 283 original papers met the inclusion criteria. The included studies focused on investigating molecular biomarkers as predictors of transformation or as prognostic markers of time-related endpoints (survival, progression, etc.). The effects of each biomarker were categorized based on their impact on prognosis or risk of transformation as none, favorable, or inferior. The biomarkers included genetic abnormalities, gene expression, microRNAs, markers of B cells/FL tumor cells, markers of the tumor microenvironment, and soluble biomarkers. This comprehensive review provides an overview of the research conducted in the past four decades, underscoring the persistent challenge in risk anticipation of FL patients.

MYC/BCL2 double- and MYC/BCL2/BCL6 triple-hit follicular lymphomas associated with t(8;14;18)(q24;q32;q21)

We describe two follicular lymphoma (FL) patients with MYC/BCL2 double- and MYC/BCL2/BCL6 triple-hit translocations. The first patient (case 1) was a man in his 30s who presented with stage IV disease with leukemic manifestation. The second patient (case 2) was a man in his 60s who presented with relapsed FL, but his disease was in a limited stage. Histopathology of the lymph node biopsies revealed grade 3A FL in both cases. MYC positivity and the Ki-67-labeling index were 60-70 and 20% in case 1 and 30 and 50% in case 2, respectively. G-banding revealed t(8;14;18)(q24;q32;q21) in both cases and fluorescence in situ hybridization using MYC, IGH, and BCL2 break-apart probes confirmed t(8;14;18)(+5'BCL2,-3'MYC;+3'MYC,-5'IGH;+5'IGH,-5'BCL2). In case 2, additional materials of der(8)t(8;14;18) were duplicated and translocated to chromosome Y, and t(3;16)(q27;p13)/BCL6::CIITA was identified. We obtained BCL2-major breakpoint region::IGHJ5::IGHG1 and MYC exon 2::IGHA2 fusion sequences by long-distance polymerase chain reaction in case 1, and proposed that t(8;14;18) was generated by two-step translocations and that BCL2::IGH and MYC::IGH involved the same IGH allele. Both patients responded to the standard chemotherapy for FL. We suggest that the presence of t(8;14;18) in FL does not immediately indicate high-grade transformation and aggressive clinical behavior requiring intensive chemotherapy.

Follicular lymphoma: updates for pathologists

Follicular lymphoma (FL) is the most common indolent B-cell lymphoma and originates from germinal center B-cells (centrocytes and centroblasts) of the lymphoid follicle. Tumorigenesis is believed to initiate early in precursor B-cells in the bone marrow (BM) that acquire the t(14;18)(q32;q21). These cells later migrate to lymph nodes to continue their maturation through the germinal center reaction, at which time they acquire additional genetic and epigeneticabnormalities that promote lymphomagenesis. FLs are heterogeneous in terms of their clinicopathologic features. Most FLs are indolent and clinically characterized by peripheral lymphadenopathy with involvement of the spleen, BM, and peripheral blood in a substantial subset of patients, sometimes accompanied by constitutional symptoms and laboratory abnormalities. Diagnosis is established by the histopathologic identification of a B-cell proliferation usually distributed in an at least partially follicular pattern, typically, but not always, in a lymph node biopsy. The B-cell proliferation is biologically of germinal center cell origin, thus shows an expression of germinal center-associated antigens as detected by immunophenotyping. Although many cases of FLs are typical and histopathologic features are straightforward, the biologic and histopathologic variability of FL is wide, and an accurate diagnosis of FL over this disease spectrum requires knowledge of morphologic variants that can mimic other lymphomas, and rarely non-hematologic malignancies, clinically unique variants, and pitfalls in the interpretation of ancillary studies. The overall survival for most patients is prolonged, but relapses are frequent. The treatment landscape in FL now includes the application of immunotherapy and targeted therapy in addition to chemotherapy.

Adverse outcome in follicular lymphoma is associated with MYC rearrangements but not MYC extra copies

Follicular lymphomas (FLs) with MYC rearrangements (MYC-R) and extra copies of MYC (MYC-EC) are rare and the prognosis impact is uncertain. We conducted a retrospective study including 321 FL patients, among whom 259 (81%) had no 8q24 alterations and 62 (19%) were assigned to 8qAlt. Forty-five cases were classified as MYC-EC and six as MYC-R. MYC-R patients were significantly older (P = 0·008), had higher follicular lymphoma international prognostic index (FLIPI) stage (P = 0·05) and β2-microglobulin (β2m; P = 0·05). Among patients treated with immuno-chemotherapy, four presented a MYC-R and 25 a MYC-EC. Univariate analysis showed the absence of significant difference between MYC-EC and normal MYC (MYC-NL) regarding progression-free survival (PFS; HR1·3; 95% CI [0·4-1·6]) and specific overall survival (SOS; HR 1·6; 95% CI [0·4-5·7]). Those results were compared to data from the PRIMA trial. This confirmed that MYC-EC had no impact on PFS (P = 0·86) or SOS (P = 0·9). Conversely, MYC-R was associated with a trend to inferior outcome regarding PFS (HR : 6·1; 95% CI [2·2-17·1]; P = 0·00026), lymphoma-related death (SOS; HR 13·6; 95% CI [2·9-65]; P = 0·00014) and risk of transformation (transformation-free survival (TFS); HR 82·7; 95% CI [14·8-463·4]; P < 0·0001). In conclusion, MYC-EC has no prognostic impact in FL but MYC-R FL tended to be associated with an increased risk of transformation and poorer outcome.

Clinicopathological and prognostic significance of BCL2, BCL6, MYC, and IRF4 copy number gains and translocations in follicular lymphoma: a study by FISH analysis

BCL2 translocation is the genetic hallmark of follicular lymphoma (FL). Besides BCL2 translocation, copy number (CN) gains and translocations of BCL6, MYC, and IRF4 have also been detected in FL, but there is little information regarding their prognostic significance. This retrospective study used fluorescence in situ hybridization (FISH) to analyze BCL2, BCL6, MYC, and IRF4 translocations and CN gains in 105 FL cases. Genetic translocations were detected for BCL2 (n = 64; 72.7%), BCL6 (n = 14; 15.9%), and MYC (n = 2; 2.3%); no case showed IRF4 translocation. Overall, 23 (26.1%), 30 (34.1%), 12 (13.8%), and 10 (11.0%) cases showed CN gains in BCL2, BCL6, MYC, and IRF4, respectively. BCL6 CN gain was a prognostic factor for worse overall survival, demonstrating a trend toward significance in multivariate analysis (HR =8.769, p = 0.056). BCL6 CN gain in FL might be associated with aggressive biologic behavior.

Pathology and diagnosis of follicular lymphoma and related entities

Follicular lymphoma (FL) is an indolent, mature B-cell neoplasm classically characterised by the t(14;18)(q32;q21) with constitutive overexpression of the anti-apoptotic protein, BCL2. Most cases present in older adults with slowly progressive lymphadenopathy and follow an indolent clinical course. Typical morphology shows an expansile follicular proliferation with tumour expression of germinal centre markers, and bone marrow involvement at diagnosis is frequent. However, in the recent past, efforts to understand the biological and clinical heterogeneity of FL has effected significant change to the diagnostic approach. While morphological grade, assessed by enumerating large 'centroblasts' in the neoplastic follicles, generally correlates with outcome in systemic nodal FL, variants with high-grade morphology but indolent clinical behaviour have been identified. Given the clinical implications of these FL variants, knowledge of their clinical and histopathological defining features is of paramount importance to the pathologist. Furthermore, as with many areas of diagnostic oncology, precursors to FL have been identified and described with measurable rates of progression to bona fide lymphoma. Accurate diagnosis of these early lesions can often prevent unnecessary therapy and guide appropriate monitoring for disease progression. This review aims to summarise these key pathological and diagnostic features of FL. We further highlight the biological underpinnings of FL that will likely affect the classification, diagnosis, and treatment of patients with lymphoma.

Del17p does not always significantly influence the survival of B-cell chronic lymphoproliferative disorders

B-cell chronic lymphoproliferative disorders (B-CLPD) comprise several entities with indolent clinical manifestations but heterogeneous survival. Cytogenetic aberrations are now the standard prognostic predictors in chronic lymphocytic leukemia (CLL) but have been less investigated in other subtypes of B-CLPD. In this study, we detected cytogenetic aberrations by fluorescence in situ hybridization (FISH) in 875 B-CLPD patients, based on a panel probes locating at 13q14, 11q22, 17p13 and CEP12. We identified del17p acted as the independent adverse cytogenetic predictor for overall survival (OS) in CLL. Del13q, del11q and del17p were adverse factors for OS in Waldenström's macroglobulinemia in the univariate analysis but lost their role in the multivariate analysis. Trisomy 12 acted as an independent poor factor for both marginal zone lymphoma (MZL) and unclassified B-CLPD (BCLPD-U) subtype. Del17p did not impact survival in MZL and BCLPD-U patients. These contrasting results indicate different roles of the same cytogenetic aberrations in the pathogenesis of each B-CLPD subtype. As del17p contributed to the poorest survival in CLL and desired extraordinary treatment strategy, the imitation of CLL strategy to other B-CLPD with del17p should be carefully advocated based on this study.

Pathogenesis of follicular lymphoma

Follicular lymphoma (FL) is presented as a germinal centre B cell lymphoma that is characterized by an indolent clinical course, but remains - paradoxically - largely incurable to date. The last years have seen significant progress in our understanding of FL lymphomagenesis, which is a multi-step process beginning in the bone marrow with the hallmark t(14;18)(q32;q21) translocation. The pathobiology of FL is complex and combines broad somatic changes at the level of both the genome and the epigenome, the latter evidenced by highly recurrent mutations in chromatin-modifying genes such as KMT2D and CREBBP. While the importance of the FL microenvironment has since long been well understood, it has become evident that somatic lesions within tumour cells re-educate normal immune and stromal cells to their advantage. Enhanced understanding of FL pathogenesis is currently leading to refined therapeutic targeting of perturbed biology, paving the way for precision medicine in this lymphoma subtype.

Combined copy number and mutation analysis identifies oncogenic pathways associated with transformation of follicular lymphoma

Follicular lymphoma (FL) is typically an indolent disease, but 30-40% of FL cases transform into an aggressive lymphoma (tFL) with a poor prognosis. To identify the genetic changes that drive this transformation, we sequenced the exomes of 12 cases with paired FL and tFL biopsies and identified 45 recurrently mutated genes in the FL-tFL data set and 39 in the tFL cases. We selected 496 genes of potential importance in transformation and sequenced them in 23 additional tFL cases. Integration of the mutation data with copy-number abnormality (CNA) data provided complementary information. We found recurrent mutations of miR-142, which has not been previously been reported to be mutated in FL/tFL. The genes most frequently mutated in tFL included KMT2D (MLL2), CREBBP, EZH2, BCL2 and MEF2B. Many recurrently mutated genes are involved in epigenetic regulation, the Janus-activated kinase-signal transducer and activator of transcription (STAT) or the nuclear factor-κB pathways, immune surveillance and cell cycle regulation or are TFs involved in B-cell development. Of particular interest are mutations and CNAs affecting S1P-activated pathways through S1PR1 or S1PR2, which likely regulate lymphoma cell migration and survival outside of follicles. Our custom gene enrichment panel provides high depth of coverage for the study of clonal evolution or divergence.

Detection of chromosomal abnormalities by G-banding and prognostic impact in follicular lymphoma in the rituximab era

Disease-specific cytogenetic abnormalities involving BCL2 gene rearrangement frequently co-exist with other cytogenetic abnormalities, contributing to disease progression in follicular lymphoma (FL). In the present study, we retrospectively investigated the prognostic impact of BCL2-unrelated cytogenetic abnormalities in FL. Of 139 consecutively diagnosed patients with FL at two independent institutes, metaphase spreads of tumor cells were obtained for use in G-banding analysis in 77 patients. The recurrent additional cytogenetic abnormalities included chromosome gains +5 (n = 8), +7 (n = 16), +12 (n = 10), and +X (n = 12), and losses -8 (n = 7), -13 (n = 12) -15 (n = 7), and 6q- (n = 7). While -15 was associated with shorter progression-free survival (PFS) in all 77 analyzed patients with evaluable G-banding results (p = 0.04), this negative impact was not evident in 42 patients treated using an R-CHOP-like regimen as first-line treatment. By contrast, 6q- was predictive for shorter PFS in patients who were initially treated with R-CHOP-like regimens without maintenance therapy (p < 0.01), while this negative impact was not evident in all 77 patients with evaluable G-banding results. These results suggest the presence of a molecular region in chromosome 6q that is responsible for the shorter PFS following R-CHOP-like chemotherapy.

Histological Transformation and Progression in Follicular Lymphoma: A Clonal Evolution Study

BACKGROUND

Follicular lymphoma (FL) is an indolent, yet incurable B cell malignancy. A subset of patients experience an increased mortality rate driven by two distinct clinical end points: histological transformation and early progression after immunochemotherapy. The nature of tumor clonal dynamics leading to these clinical end points is poorly understood, and previously determined genetic alterations do not explain the majority of transformed cases or accurately predict early progressive disease. We contend that detailed knowledge of the expansion patterns of specific cell populations plus their associated mutations would provide insight into therapeutic strategies and disease biology over the time course of FL clinical histories.

METHODS AND FINDINGS

Using a combination of whole genome sequencing, targeted deep sequencing, and digital droplet PCR on matched diagnostic and relapse specimens, we deciphered the constituent clonal populations in 15 transformation cases and 6 progression cases, and measured the change in clonal population abundance over time. We observed widely divergent patterns of clonal dynamics in transformed cases relative to progressed cases. Transformation specimens were generally composed of clones that were rare or absent in diagnostic specimens, consistent with dramatic clonal expansions that came to dominate the transformation specimens. This pattern was independent of time to transformation and treatment modality. By contrast, early progression specimens were composed of clones that were already present in the diagnostic specimens and exhibited only moderate clonal dynamics, even in the presence of immunochemotherapy. Analysis of somatic mutations impacting 94 genes was undertaken in an extension cohort consisting of 395 samples from 277 patients in order to decipher disrupted biology in the two clinical end points. We found 12 genes that were more commonly mutated in transformed samples than in the preceding FL tumors, including TP53, B2M, CCND3, GNA13, S1PR2, and P2RY8. Moreover, ten genes were more commonly mutated in diagnostic specimens of patients with early progression, including TP53, BTG1, MKI67, and XBP1.

CONCLUSIONS

Our results illuminate contrasting modes of evolution shaping the clinical histories of transformation and progression. They have implications for interpretation of evolutionary dynamics in the context of treatment-induced selective pressures, and indicate that transformation and progression will require different clinical management strategies.

B-Lymphoblastic Lymphomas Evolving from Follicular Lymphomas Co-Express Surrogate Light Chains and Mutated Gamma Heavy Chains

Follicular lymphoma (FL) is an indolent B-cell non-Hodgkin lymphoma able to transform into germinal center-type diffuse large B-cell lymphoma. We describe four extraordinary cases of FL, which progressed to TdT⁺CD20^- precursor B-lymphoblastic lymphoma (B-LBL). Fluorescence in situ hybridization analysis showed that all four B-LBLs had acquired a MYC translocation on transformation. Comparative genomic hybridization analysis of one case demonstrated that in addition to 26 numerical aberrations that were shared between the FL and B-LBL, deletion of CDKN2A/B and 17q11, 14q32 amplification, and copy-neutral loss of heterozygosity of 9p were gained in the B-LBL cells. Whole-exome sequencing revealed mutations in FMN2, NEB, and SYNE1 and a nonsense mutation in KMT2D, all shared by the FL and B-LBL, and TNFRSF14, SMARCA2, CCND3 mutations uniquely present in the B-LBL. Remarkably, all four FL-B-LBL pairs expressed IgG. In two B-LBLs, evidence was obtained for ongoing rearrangement of IG light chain variable genes and expression of the surrogate light chain. IGHV mutation analysis showed that all FL-B-LBL pairs harbored identical or near-identical somatic mutations. From the somatic gene alterations found in the IG and non-IG genes, we conclude that the FLs and B-LBLs did not develop in parallel from early t(14;18)-positive IG-unmutated precursors, but that the B-LBLs developed from preexistent FL subclones that accumulated additional genetic damage.

CD5-positive follicular lymphoma: clinicopathologic correlations and outcome in 88 cases

Follicular lymphoma is a low-grade B-cell lymphoma of germinal center B-cell origin that typically lacks CD5 expression. We describe the clinicopathologic features of 88 cases of CD5+ follicular lymphoma (53 men, 35 women; median age, 60 years; range, 31-86). Follicular lymphoma was diagnosed initially in lymph nodes in 66 and extranodal sites in 22 patients. Eighty-one patients had lymphadenopathy, 66 had more than one involved site, 46 had bone marrow involvement, and 7 had splenomegaly. Staging information was available for 84 patients: 52 stage IV, 18 stage III, 12 stage II, and 2 stage I. Sixty-one cases were grade 1 or 2 and 27 were grade 3. The median proliferation index (Ki-67) was 30%. CD5 expression was detected by flow cytometry in 69, immunohistochemistry in 8, and both methods in 11 cases. The presence of t(14;18)(q32;q21)/IGH-BCL2 or other BCL2 translocation was detected in 28/44 (64%) cases. A total of 38 (43%) patients also had diffuse large B-cell lymphoma, concurrent with (n=20), subsequent to (n=13), or developing before CD5+ follicular lymphoma (n=5). All patients received chemotherapy; 12 also received stem-cell transplantation. With a median follow-up of 55 months (range, 0.5-207), 15 patients died, 46 were alive with disease, and 20 were in clinical remission. Compared with a matched group of patients with CD5- follicular lymphoma, patients with CD5+ follicular lymphoma more commonly had an International Prognostic Index >2 (35/80 vs 10/99, P<0.001), more often developed diffuse large B-cell lymphoma (38/88 vs 17/99; P<0.001), and had a shorter median progression-free survival (44 vs 89 months, P=0.0042). Higher Ki-67 and International Prognostic Index were identified as poor prognostic factors in both the groups. We conclude that CD5 expression in follicular lymphoma is associated with a higher International Prognostic Index, higher rate of transformation to diffuse large B-cell lymphoma, and shorter progression-free survival.

Mechanisms and clinical applications of chromosomal instability in lymphoid malignancy

Lymphocytes are unique among cells in that they undergo programmed DNA breaks and translocations, but that special property predisposes them to chromosomal instability (CIN), a cardinal feature of neoplastic lymphoid cells that manifests as whole chromosome- or translocation-based aneuploidy. In several lymphoid malignancies translocations may be the defining or diagnostic markers of the diseases. CIN is a cornerstone of the mutational architecture supporting lymphoid neoplasia, though it is perhaps one of the least understood components of malignant transformation in terms of its molecular mechanisms. CIN is associated with prognosis and response to treatment, making it a key area for impacting treatment outcomes and predicting prognoses. Here we will review the types and mechanisms of CIN found in Hodgkin lymphoma, non-Hodgkin lymphoma, multiple myeloma and the lymphoid leukaemias, with emphasis placed on pathogenic mutations affecting DNA recombination, replication and repair; telomere function; and mitotic regulation of spindle attachment, centrosome function, and chromosomal segregation. We will discuss the means by which chromosome-level genetic aberrations may give rise to multiple pathogenic mutations required for carcinogenesis and conclude with a discussion of the clinical applications of CIN and aneuploidy to diagnosis, prognosis and therapy.

Telomeric 1p36.3 deletion and Ki-67 expression in B-Non-Hodgkin's Lymphoma patients associated with chronic hepatitis C virus infection

The hepatitis C virus (HCV) core protein is able to accumulate genetic p53 mutations and may be considered co-oncogenic. This study investigates 1p36.3 telomere deletion in B-non-Hodgkin's lymphoma (NHL) patients with chronic HCV infection using fluorescence in situ hybridization (FISH) in relation to survival to assess Ki-67 antigen expression. A study group and a control group of 100 patients with B-NHL (50 HCV positive and 50 HCV negative) and 60 control bone marrow biopsies were subjected to FISH for the detection of 1P36.3 deletion and to immunohistochemical staining with Ki-67 antigens. 1p36.3 deletion by FISH was detected in 40% of the study group, and Ki-67 was expressed in approximately 74% of patients. A significant difference was found between positive and negative HCV patients in their overall survival, the qualitative expression of Ki-67 and the quantitative detection of 1p36.3 deletion by FISH. The overall survival was shorter with the presence of an 1p36 deletion by FISH and HCV positive. We concluded that the coexistence of Ki-67 positivity, HCV positivity and 1p36.3 deletion may contribute to infection-related cancers at the 1p36.3 locus.

Mutations in linker histone genes HIST1H1 B, C, D, and E; OCT2 (POU2F2); IRF8; and ARID1A underlying the pathogenesis of follicular lymphoma

Follicular lymphoma (FL) constitutes the second most common non-Hodgkin lymphoma in the western world. FL carries characteristic recurrent structural genomic aberrations. However, information regarding the coding genome in FL is still evolving. Here, we describe the results of massively parallel exome sequencing and single nucleotide polymorphism 6.0 array genomic profiling of 11 highly purified FL cases, and 1 transformed FL case and the validation of selected mutations in 102 FL cases. We report the identification of 15 novel recurrently mutated genes in FL. These include frequent mutations in the linker histone genes HIST1H1 B-E (27%) and mutations in OCT2 (also known as POU2F2; 8%), IRF8 (6%), and ARID1A (11%). A subset of the mutations in HIST1H1 B-E affected binding to DNMT3B, and mutations in HIST1H1 B-E and in EZH2 or ARID1A were largely mutually exclusive, implicating HIST1H1 B-E in epigenetic deregulation in FL. Mutations in OCT2 (POU2F2) affected its transcriptional and functional properties as measured through luciferase assays, the biological analysis of stably transduced cell lines, and global expression profiling. Finally, multiple novel mutated genes located within regions of acquired uniparental disomy in FL are identified. In aggregate, these data substantially broaden our understanding of the genomic pathogenesis of FL.

Early lesions of follicular lymphoma: a genetic perspective

The pathogenesis of follicular lymphoma is a multi-hit process progressing over many years through the accumulation of numerous genetic alterations. Besides the hallmark t(14;18), it is still unclear which other oncogenic hits contribute to the early steps of transformation and in which precursor stages these occur. To address this issue, we performed high-resolution comparative genomic hybridization microarrays on laser-capture micro-dissected cases of follicular lymphoma in situ (n=4), partial involvement by follicular lymphoma (n=4), and duodenal follicular lymphoma (n=4), assumed to represent, potentially, the earliest stages in the evolution of follicular lymphoma. Cases of reactive follicular hyperplasia (n=2), uninvolved areas from follicular lymphoma in situ lymph nodes, follicular lymphoma grade 1-2 (n=5) and follicular lymphoma grade 3A (n=5) were used as controls. Surprisingly, alterations involving several relevant (onco)genes were found in all entities, but at significantly lower proportions than in overt follicular lymphoma. While the number of alterations clearly assigns all these entities as precursors, the pattern of partial involvement by follicular lymphoma alterations was quantitatively and qualitatively closer to that of follicular lymphoma, indicating significant selective pressure in line with its faster rate of progression. Among the most notable alterations, we observed and validated deletions of 1p36 and gains of the 7p and 12q chromosomes and related oncogenes, which include some of the most recurrent oncogenic alterations in overt follicular lymphoma (TNFRSF14, EZH2, MLL2). By further delineating distinctive and hierarchical molecular and genetic features of early follicular lymphoma entities, our analysis underlines the importance of applying appropriate criteria for the differential diagnosis. It also provides a first set of candidates likely to be involved in the cascade of hits that pave the path of the various progression phases to follicular lymphoma development.

Differences in the cytogenetic alteration profiles of diffuse large B-cell lymphoma among Chinese and American patients

To study the similarities and differences of cytogenetic alterations in diffuse large B-cell lymphoma (DLBCL) between Asian and Caucasian patients, we compared the cytogenetic profiles of Chinese and American DLBCL cases by analyzing conventional karyotypes and select fluorescence in situ hybridization (FISH) findings. We used interphase FISH analyses to determine the incidence of the t(14;18) and BCL6 and MYC rearrangements. Immunohistochemical analysis was used to categorize the lymphomas into the germinal center B-cell-like (GCB) or non-GCB-DLBCL subtypes, according to the Hans algorithm. Our data suggested that Chinese patients had cytogenetic profiles for GCB-DLBCL that differed from those of their American counterparts; specifically, the Chinese GCB patients exhibited greater frequencies of BCL6 rearrangements and gains of 1q and 11q but lower incidence of the t(14;18). Non-GCB-DLBCL in both the Chinese and American patients was characterized by recurrent gains of 3/3q and 18/18q. The incidences of both BCL6 rearrangement and t(14;18) were similar in Chinese and American non-GCB-DLBCL cases.

Genome-wide copy-number analyses reveal genomic abnormalities involved in transformation of follicular lymphoma

Follicular lymphoma (FL), the second most common type of non-Hodgkin lymphoma in the western world, is characterized by the t(14;18) translocation, which is present in up to 90% of cases. We studied 277 lymphoma samples (198 FL and 79 transformed FL [tFL]) using a single-nucleotide polymorphism array to identify the secondary chromosomal abnormalities that drive the development of FL and its transformation to diffuse large B-cell lymphoma. Common recurrent chromosomal abnormalities in FL included gains of 2, 5, 7, 6p, 8, 12, 17q, 18, 21, and X and losses on 6q and 17p. We also observed many frequent small abnormalities, including losses of 1p36.33-p36.31, 6q23.3-q24.1, and 10q23.1-q25.1 and gains of 2p16.1-p15, 8q24.13-q24.3, and 12q12-q13.13, and identified candidate genes that may be driving this selection. Recurrent abnormalities more frequent in tFL samples included gains of 3q27.3-q28 and chromosome 11 and losses of 9p21.3 and 15q. Four abnormalities, gain of X or Xp and losses of 6q23.2-24.1 or 6q13-15, predicted overall survival. Abnormalities associated with transformation of the disease likely impair immune surveillance, activate the nuclear factor-κB pathway, and deregulate p53 and B-cell transcription factors.

The 3q27 and 18q21 translocations for follicular lymphoma and diffuse large B-cell lymphoma in the rituximab era

The 3q27 and 18q21 chromosomal translocations are major hallmarks in B-cell lymphoma. We aimed to determine the frequencies of these translocations in follicular lymphoma (FL) and diffuse large B-cell lymphoma (DLBCL) and to evaluate their prognostic impact in the rituximab era. This study included 98 FL and 93 DLBCL patients whose abnormal karyotypes had been detected using G-banding. Patients uniformly underwent R-CHOP therapy : doxorubicin, cyclophosphamide, vincristine, prednisolone, and rituximab ; survivors were followed up for 29 months (median). The 3q27 and 18q21 translocations were detected in 14 and 77 FL patients and 14 and 22 DLBCL patients, respectively. Overall survival (OS) and progression-free survival (PFS) did not differ significantly between the groups with 3q27, 18q21, concurrent 3q27 and 18q21 translocations, and other chromosomal abnormalities for FL and DLBCL. There were no significant differences in OS and PFS between patients with 3q27 translocation-positive FL and those with 3q27 translocation-positive DLBCL or between the patients with 18q21 translocation-positive FL and those with 18q21 translocation-positive DLBCL. The presence of 3q27 and 18q21 translocations did not correlate with the clinical outcomes of FL or DLBCL patients following R-CHOP treatment.

Dissecting the gray zone between follicular lymphoma and marginal zone lymphoma using morphological and genetic features

Nodal marginal zone lymphoma is a poorly defined entity in the World Health Organization classification, based largely on criteria of exclusion and the diagnosis often remains subjective. Follicular lymphoma lacking t(14;18) has similar characteristics which results in a major potential diagnostic overlap which this study aims to dissect. Four subgroups of lymphoma samples (n=56) were analyzed with high-resolution array comparative genome hybridization: nodal marginal zone lymphoma, t(14;18)-negative follicular lymphoma, localized t(14:18)-positive follicular lymphoma and disseminated t(14;18)-positive follicular lymphoma. Gains on chromosomes 7, 8 and 12 were observed in all subgroups. The mean number of aberrations was higher in disseminated t(14;18)-positive follicular lymphoma than in localized t(14:18)-positive follicular lymphoma (P<0.01) and the majority of alterations in localized t(14:18)-positive follicular lymphoma were also found in disseminated t(14;18)-positive follicular lymphoma. Nodal marginal zone lymphoma was marked by 3q gains with amplifications of four genes. A different overall pattern of aberrations was seen in t(14;18)-negative follicular lymphoma compared to t(14;18)-positive follicular lymphoma. t(14;18)-negative follicular lymphoma is characterized by specific (focal) gains on chromosome 3, as observed in nodal marginal zone lymphoma. Our results support the notion that localized t(14:18)-positive follicular lymphoma represents an early phase of disseminated t(14;18)-positive follicular lymphoma. t(14;18)-negative follicular lymphoma bears aberrations that are more like those in nodal marginal zone lymphoma, suggesting a relation between these groups.

6q deletion detected by fluorescence in situ hybridization using bacterial artificial chromosome in chronic lymphocytic leukemia

Deletions of the long arm of chromosome 6 are known to occur at relatively low frequency (3-6%) in chronic lymphocytic leukemia (CLL), and they are more frequently observed in 6q21. Few data have been reported regarding other bands on 6q involved by cytogenetic alterations in CLL. The cytogenetic study was performed in nuclei and metaphases obtained after stimulation with a combination of CpG-oligonucleotide DSP30 and interleukin-2. Four bacterial artificial chromosome (BAC) clones mapping regions in bands 6q16, 6q23, 6q25, 6q27 were used as probes for fluorescence in situ hybridization in 107 CLL cases in order to analyze the occurrence and localization of 6q aberrations. We identified 11 cases (10.2%) with 6q deletion of 107 patients studied with CLL. The trends of survival curves and the treatment-free intervals (TFI) of patients with deletion suggest a better outcome than the other cytogenetic risk groups. We observed two subgroups with 6q deletion as the sole anomaly: two cases with 6q16 deletion, and three cases with 6q25.2-27 deletion. There were differences of age, stage, and TFI between both subgroups. By using BAC probes, we observed that 6q deletion has a higher frequency in CLL and is linked with a good prognosis. In addition, it was observed that the deletion in 6q16 appears to be the most frequent and, if present as the only abnormality, it could be associated with a most widespread disease.

Refinement of 1p36 alterations not involving PRDM16 in myeloid and lymphoid malignancies

Fluorescence in situ hybridization was performed to characterize 81 cases of myeloid and lymphoid malignancies with cytogenetic 1p36 alterations not affecting the PRDM16 locus. In total, three subgroups were identified: balanced translocations (N = 27) and telomeric rearrangements (N = 15), both mainly observed in myeloid disorders; and unbalanced non-telomeric rearrangements (N = 39), mainly observed in lymphoid proliferations and frequently associated with a highly complex karyotype. The 1p36 rearrangement was isolated in 12 cases, mainly myeloid disorders. The breakpoints on 1p36 were more widely distributed than previously reported, but with identifiable rare breakpoint cluster regions, such as the TP73 locus. We also found novel partner loci on 1p36 for the known multi-partner genes HMGA2 and RUNX1. We precised the common terminal 1p36 deletion, which has been suggested to have an adverse prognosis, in B-cell lymphomas [follicular lymphomas and diffuse large B-cell lymphomas with t(14;18)(q32;q21) as well as follicular lymphomas without t(14;18)]. Intrachromosomal telomeric repetitive sequences were detected in at least half the cases of telomeric rearrangements. It is unclear how the latter rearrangements occurred and whether they represent oncogenic events or result from chromosomal instability during oncogenesis.

Chromosome abnormalities defined by conventional cytogenetics in plasma cell leukemia: what have we learned about its biology?

Cancer cells are characterized by having chromosomal abnormalities. The number of aberrations and the specific chromosomes affected are likely correlated with tumor progression. In this study, we analyzed the karyotype of 126 plasma cell leukemia (PCL) patients to identify the most frequently occurring imbalances and to design a model of karyotypic evolution. The Mitelman database of chromosome was searched and abnormal karyotypes were assessed. The main clones were analyzed and chromosomal gains and losses were used to design a model of genetic acquisition based on the calculation of a variable called time to occurrence. Our comprehensive study of genetic abnormalities of a large number of PCL karyotypes suggests that PCL is mainly characterized by the presence of whole chromosome losses as well as IgH rearrangements which is similar to that observed in non-hyperdiploid multiple myeloma (MM). Temporal analysis suggests that most PCL have around 10 abnormalities at diagnosis. It is possible that accumulation of abnormalities such as 17p13 (TP53) and 1p losses may trigger the extramedullary features of PCL. Our study demonstrates that cytogenetics is a valuable tool to evaluate the role of genetic imbalances on karyotypic evolution by using a mathematical model.

Transformation of follicular lymphoma

Histological transformation of follicular lymphoma (FL) to a more aggressive non-Hodgkin's lymphomas is a pivotal event in the natural history of FL and is associated with poor outcome. While commonly observed in clinical practice and despite multiple studies designed to address its pathogenesis, the biology of this process represents an enigma. In this chapter we present a state of the art review summarizing the definition of histologic transformation, its incidence, pathogenesis, clinical manifestations, treatment and outcome. Furthermore, we specifically emphasize gaps in our knowledge that should be addressed in future studies.

Pathogenesis of non-Hodgkin's lymphoma

The understanding of the molecular pathogenesis of non-Hodgkin's lymphomas (NHL) has significantly improved in recent years. Advances in molecular biology and genetics lead to the identification and characterization of several oncogenic pathways involved in lymphomagenesis. This knowledge will ultimately lead to improved diagnostic and therapeutic strategies for patients with NHL. This review summarizes current concepts of the molecular pathogenesis of the most common NHL subtypes, with a special emphasis on diffuse large B-cell lymphoma, the most common lymphoma subtype.

Pathology, pathogenesis and molecular genetics of follicular NHL

Follicular lymphoma (FL) is a germinal centre-derived indolent B-cell lymphoma representing the second most common Non Hodgkin lymphoma in the Western world. This chapter focuses on the pathology of FL and summarizes the current knowledge about genetic and molecular features that are relevant for the pathogenesis of this neoplasm. The translocation t(14;18) is present in approximately 90% of FL leading to the upregulation of the anti-apoptotic protein BCL2, that may constitute a promising molecular target for therapeutic approaches. FL lacking the t(14;18) also exist, and B-cells carrying the t(14;18) can be detected in a subset of healthy individuals. In addition to the t(14;18), secondary genetic alterations are present in most FL and, more recently, deeper insights into the methylation and microRNA expression patterns in the tumour cells have been gained. The tumour microenvironment appears to be particularly important for the biology and the clinical course of FL.

Integrated profiling of diffuse large B-cell lymphoma with 7q gain

To characterize diffuse large B-cell lymphoma (DLBCL) with chromosome 7 gains, we combined clinical data with genomic, RNA and miRNA profiling. Gains were associated with age >60 years, female gender, a trend for higher complete response rate, lower death rate, and better overall survival in patients treated with R-CHOP. Lesions were inversely associated with bone marrow involvement and number of extra-nodal sites. Differentially expressed transcripts were enriched of genes belonging to specific pathways and miRNAs targets. MIR96, MIR182, MIR589, MIR25 were shown significantly up-regulated in 7q+ DLBCL by real-time PCR.

Primary follicular lymphoma of the duodenum is a distinct mucosal/submucosal variant of follicular lymphoma: a retrospective study of 63 cases

PURPOSE

Small series with limited follow-up have suggested primary follicular lymphoma of the duodenum (FL-D) to be an indolent disease. We report our experience on a large series of patients followed for a median time period of longer than 6 years.

PATIENTS AND METHODS

The study comprised 63 patients with primary FL-D defined as stage I disease. Endoscopy and detailed pathologic work-up was performed at diagnosis and at restaging to monitor the behavior of the neoplastic process.

RESULTS

Histologically, all 63 patients had FL, low grade (1 to 2). Duodenal endosonography demonstrated lesions confined to mucosa/submucosa in 19 of 20 patients. At an overall median follow-up of 77 months (range, 12 to 177 months), only two untreated patients had developed nodal disease, the remaining 61 patients never experienced extrasmall intestinal disease and large cell transformation did not occur at all. Among 24 patients followed by watch and wait strategy, seven showed spontaneous complete regression and 17 had stable disease; radiotherapy resulted in complete regression in all 19 patients; anti-CD20 antibody monotherapy achieved complete regression in four patients and stable disease in one patient. Various chemotherapy protocols in eight patients caused complete regression in all of them, but local relapses occurred in three. No patients required surgery or died of disease.

CONCLUSION

These findings characterize primary FL-D as a remarkably indolent FL variant, which, even left untreated, does not develop tumorous growth, very rarely disseminates (two of 63 patients) and does not transform to high grade disease. A watch and wait approach appears to be the most sensible strategy.

Prognostic biomarkers in malignant lymphomas

There has recently been a rapid expansion in research aimed at identifying biomarkers that could improve the prognosis for patients with various subtypes of malignant lymphoma. Genomic and genetic studies have led to the identification of biological and clinical subgroups of diffuse large B-cell lymphomas with distinct underlying molecular features, divergent activation of oncogenetic pathways, and clinical course. Molecular studies of follicular lymphoma have suggested complex interactions between malignant cells and the surrounding immunological network that could affect disease progression. Moreover, the inflammatory cells of Hodgkin lymphoma have been shown to produce a complex network of cytokines and chemokines that provide a permissive microenvironment for tumor growth. Research into specific biomarkers and signaling pathways of malignant lymphomas might therefore result in the identification of novel targets for future therapeutic strategies. As gene expression profiling techniques are not yet feasible in the clinical laboratory, studies have aimed to translate the findings into more widely applicable techniques that might allow this research to be applied to routine clinical practice. This review focuses on recent advances in translational and clinical research on biomarkers in malignant lymphomas.

Genomic alterations reveal potential for higher grade transformation in follicular lymphoma and confirm parallel evolution of tumor cell clones

Our aim was to examine the genetics of clonal evolution in follicular lymphoma (FL) and to identify genetic alterations associated with disease progression. A total of 100 biopsies from 44 patients diagnosed with t(14;18)-positive FL were examined by array comparative genomic hybridization. In 20 patients the patterns of somatic hypermutations (SHMs) in the variable region of heavy chain gene were additionally analyzed. Gain of chromosome X in male samples was a marker for poor outcome (P < .01). Gains involving chromosome 2, 3q, and 5 were exclusively present in FL biopsies from cases with higher grade transformation and were among the copy number alterations (CNAs) associated with inferior survival. Although we noted a trend for increasing genomic complexity in initial versus late FL samples, the overall frequencies of CNAs in initial and late FL biopsies showed a surprisingly stable pattern through the course of the disease. In 27 of cases the initial samples harbored CNAs that were absent in relapse samples, indicating that tumor cell clones at relapse were not direct descendants of initially dominating clones. The pattern of SHMs confirmed parallel development of tumor cell clones in 14 cases. Our findings support the hypothesis of common progenitor cells in FL.

Cytogenetic analysis of pediatric anaplastic large cell lymphoma

BACKGROUND

Anaplastic large cell lymphoma (ALCL) constitutes approximately 15% of pediatric and 3% of adult non-Hodgkin lymphomas. Most pediatric cases harbor the reciprocal translocation t(2;5)(p23;q35), involving the alk gene. Cytogenetic studies of ALCL have mostly been published as case-reports. The aim of this study was to determine the cytogenetic profiles of a series of pediatric ALCL and to compare them with pediatric and adult ALCL from the literature.

METHODS

Eighteen children treated at our Institution were studied by standard cytogenetic analysis and RT-PCR for the specific t(2;5) translocation product. Comparative analysis was performed on our findings and on the karyotypes of 48 pediatric and 39 adult ALCL reported in the literature.

RESULTS

Karyotype was obtained in 16/18 ALCL: 9 showed translocation t(2;5) and 1 an alk variant form. Structural and numeric chromosomal abnormalities were identified in both pediatric and adult series. Trisomies were found preferentially in pediatric patients (P = 0.013) and monosomies in adults (P = 0.038). Trisomy 7 was found in 22% (13/59) of pediatric cases with abnormal karyotype and only in 5% (2/38) of adults; monosomy of chromosome 13 in 13% (5/38) of adults and only in 2% (1/59) of pediatric patients and monosomy of chromosome 15 in 16% (6/38) of adults and in none of the pediatric ALCL.

CONCLUSION

Our data suggest that pediatric and adult ALCL are characterized by different numerical chromosomal abnormalities. Larger prospective studies may elucidate their potential prognostic impact.

Follicular lymphoma prognostic factors in the modern era: what is clinically meaningful?

Follicular lymphomas (FL) account for 30% of non-Hodgkin's lymphomas (NHL). Their evolution is heterogeneous. Some patients present with indolent forms undergoing several relapses while in other patients the disease evolves abruptly toward aggressive NHL. This is why accurate prognostic indices are required so that treatment strategies may be optimized for each patient and so that trials may be conducted in groups of patients that are as homogeneous as possible. The Follicular Lymphoma International Prognostic Index (FLIPI) has been designed to separate patients into 3 groups with significantly different hazard ratios for death. Its accuracy has been confirmed in several studies. The FLIPI2 was designed more recently to separate patients with significantly different hazard ratios for progression/relapse in the era of anti-CD20 monoclonal antibody treatments. Gene profile studies have shown that the prognosis of FL is mainly related to the type, number, and activation of immune cells in the microenvironment of lymphomatous follicles. Immunohistochemical studies suggest that macrophages, CD4+ T cells and among them T-regulatory cells (T-regs) and programed death-1 cells (PD-1 cells) play a major role in the outcome of FLs. However, additional confirmatory studies are required due to discrepancies in results. Up to now, these biological study results are more useful for approaching the pathophysiology of FL rather than to be used as prognostic tools in clinical practice.

Prognostic Factors in Follicular Lymphoma

Follicular lymphoma (FL) is one of the most common types of non-Hodgkin's lymphoma. It is usually diagnosed at an advanced stage, for which many treatment options exist, however, no curative standard therapy has been identified. The outcome is highly variable with a median survival of approximately 10 years. The life expectancy of patients with FL has been extended with the use of rituximab, a monoclonal antibody targeting the CD20 antigen on FL cells, but there remains a group of patients who fail to respond to chemoimmunotherapy and die early of their disease. Transformation of FL to an aggressive histology is an important event with high morbidity and mortality. The Follicular Lymphoma International Prognostic Index has become the clinically useful prognostic tool, but gives only a rough estimate of expected outcome. There is a need for useful biomarkers for prediction of the disease course of single patients to individualize therapy, especially in the new era of chemoimmunotherapy.

Diffuse blastoid B-cell lymphoma: a histologically aggressive variant of t(14;18)-negative follicular lymphoma

Among the diffuse lymphomas of B-cell origin, we have encountered one variant displaying blastoid features that morphologically mimic lymphoblastic lymphoma, the blastoid variant of mantle cell lymphoma, and the so-called blastoid transformation of follicular lymphoma. To better characterize this entity, we studied eight cases morphologically, immunohistochemically, and by fluorescence in situ hybridization (FISH) for cytogenetic abnormalities commonly associated with follicular lymphoma and B-cell lymphomas exhibiting high-grade histological features. All eight cases were presented as de novo neoplasms, and displayed an entirely diffuse (five cases) or only minimal follicular (three cases) growth pattern. The neoplastic lymphoid cells were of medium size with round nuclei, fine chromatin, inconspicuous nucleoli, and high mitotic rate; they expressed CD10, BCL6, and BCL2-a phenotype consistent with follicle center cell origin. A proportion of cases expressed MUM1. Their lack of TdT and CYCLIN D1 distinguished them from lymphoblastic lymphoma and the blastoid mantle cell lymphoma, respectively. The neoplastic lymphoid cells consistently expressed CD43 (seven of eight cases) and occasionally other T-cell-associated antigens, including CD5, CD7, CD8, and CD57. Although all cases overexpressed BCL2, t(14;18) was not detected in any of the five cases examined by FISH; instead, extra copies of chromosome 18 were found in four of five cases. Finally, other cytogenetic abnormalities, including structural abnormalities of BCL6 (allelic loss/gain, rearrangement), monosomy 7, del(13)(q14), and MYC allelic loss, were frequently detected. The combination of a B-cell CD10+ BCL6+ BCL2+ phenotype in the presence of structural abnormalities of BCL6 is consistent with a follicular center cell derivation for our cases. The lack of t(14;18) seen in our cases, although rare in most cases of follicular lymphoma, has been nevertheless reported in cases of follicular lymphoma with a predominantly diffuse growth pattern. The molecular pathogenesis, clinical manifestations, and prognostic significance of these lesions remain to be elucidated.

Model-based clustering of array CGH data

Motivation: Analysis of array comparative genomic hybridization (aCGH) data for recurrent DNA copy number alterations from a cohort of patients can yield distinct sets of molecular signatures or profiles. This can be due to the presence of heterogeneous cancer subtypes within a supposedly homogeneous population.

Results: We propose a novel statistical method for automatically detecting such subtypes or clusters. Our approach is model based: each cluster is defined in terms of a sparse profile, which contains the locations of unusually frequent alterations. The profile is represented as a hidden Markov model. Samples are assigned to clusters based on their similarity to the cluster's profile. We simultaneously infer the cluster assignments and the cluster profiles using an expectation maximization-like algorithm. We show, using a realistic simulation study, that our method is significantly more accurate than standard clustering techniques. We then apply our method to two clinical datasets. In particular, we examine previously reported aCGH data from a cohort of 106 follicular lymphoma patients, and discover clusters that are known to correspond to clinically relevant subgroups. In addition, we examine a cohort of 92 diffuse large B-cell lymphoma patients, and discover previously unreported clusters of biological interest which have inspired followup clinical research on an independent cohort.

Availability: Software and synthetic datasets are available at http://www.cs.ubc.ca/∼sshah/acgh as part of the CNA-HMMer package.

Contact:sshah@bccrc.ca

Supplementary information:Supplementary data are available at Bioinformatics online.

Follicular lymphoma: a historical overview

Lymphoma was first described in 1862 and follicular lymphoma in 1925. Initially considered a benign disorder, and named Brill - Symmers disease after the authors of the original papers, it was rapidly recognized as a malignancy with a variable but often indolent course. Most of its clinical features were described by the early 1940s. Despite discussion about its cell of origin, and in contrast to many other lymphoma subtypes, follicular lymphoma could always be accurately recognized and diagnosed using light microscopy morphological features. B-cell origin was demonstrated in the 1970s and the important role of t(14;18) and bcl-2 gene rearrangement in the pathogenesis of follicular lymphoma was established shortly thereafter. The etiology of follicular lymphoma, the reason for marked geographic variation in its incidence, the role of alternative molecular pathways in its pathogenesis, and the cause for its variable clinical behavior all remain unknown. Several observations suggest an important role for the normal immune response in regulating the clinical behavior of follicular lymphoma. From the earliest descriptions, radiation therapy was shown to be very effective in follicular lymphoma, but not curative. Combination chemotherapy was tested in the 1970s, but despite high rates of response, there was only minimal impact on survival. Interferon combined with anthracycline based chemotherapy was the first treatment to improve survival, but was not widely adopted in the USA. Randomized studies have shown an impact of autologous transplantation on progression free survival. Allogeneic transplantation is a curative therapy, but is too toxic for widespread application. Targeted therapies, particularly rituximab have revolutionized the treatment of follicular lymphoma. A convergence of technological and biological advances will likely lead to further dramatic progress in the next decade. For the first time consistent improvements in survival of follicular lymphoma are reported.

Regions of acquired uniparental disomy at diagnosis of follicular lymphoma are associated with both overall survival and risk of transformation

Acquired homozygosity in the form of segmental acquired uniparental disomy (aUPD) has been described in follicular lymphoma (FL) and is usually due to mitotic recombination. SNP array analysis was performed with the use of the Affymetrix 10K 2.0 Gene-chip array on DNA from 185 diagnostic FL patients to assess the prognostic relevance of aUPD. Genetic abnormalities were detected in 118 (65%) of 182 patients. Number of abnormalities was predictive of outcome; more than 3 abnormalities was associated with inferior overall survival (OS; P < .03). Sites of recurrent aUPD were detected on 6p (n = 25), 16p (n = 22), 12q (n = 17), 1p36 (n = 14), 10q (n = 8), and 6q (n = 8). On multivariate analysis aUPD on 1p36 correlated with shorter OS (P = .05). aUPD on 16p was predictive of transformation (P = .03) and correlated with poorer progression-free survival (P = .02). aUPD is frequent at diagnosis of FL and affects probability of disease transformation and clinical outcome.