High-grade B-cell lymphomas with TdT expression: a diagnostic and classification dilemma

Transformation of marginal zone lymphoma into high-grade B-cell lymphoma expressing terminal deoxynucleotidyl transferase: A case report

BACKGROUND

High-grade B-cell lymphoma (HGBL) is an unusual malignancy that includes myelocytomatosis viral oncogene (MYC), B-cell lymphoma-2 (BCL-2), and/or BCL-6 rearrangements, termed double-hit or triple-hit lymphomas, and HGBL-not otherwise specific (HGBL-NOS), which are morphologically characteristic of HGBL but lack MYC, BCL-2, or BCL-6 rearrangements. HGBL is partially transformed by follicular lymphoma and other indolent lymphoma, with few cases of marginal zone lymphoma (MZL) transformation. HGBL often has a poor prognosis and intensive therapy is currently mainly advocated, but there is no good treatment for these patients who cannot tolerate chemotherapy.

CASE SUMMARY

We reported a case of MZL transformed into HGBL-NOS with TP53 mutation and terminal deoxynucleotidyl transferase expression. Gene analysis revealed the gene expression profile was identical in the pre- and post-transformed tissues, suggesting that the two diseases are homologous, not secondary tumors. The chemotherapy was ineffective and the side effect was severe, so we tried combination therapy including venetoclax and obinutuzumab. The patient tolerated treatment well, and reached partial response. The patient had recurrence of hepatocellular carcinoma and died of multifunctional organ failure. He survived for 12 months after diagnosis.

CONCLUSION

Venetoclax combined with obinutuzumab might improve the survival in some HGBL patients, who are unsuitable for chemotherapy.

Case report: Mutation evolution in a patient with TdT positive high grade B cell lymphoma with MYC and BCL2 rearrangements following the treatment of concurrent follicular lymphoma and diffuse large B-cell lymphoma

BACKGROUND

Concurrent follicular lymphoma (FL) and diffuse large B-cell lymphoma (DLBCL)was reported in some studies, while the diagnosis of TdT (terminal deoxynucleotydil transferase) positive high grade B cell lymphoma (HGBL) with MYC and BCL2 rearrangements ("double hit") transformed from FL/DLBCL has been rarely reported. Herein, we described the clinical features and mutation profiles of a case diagnosed with TdT positive "double hit" HGBL following the treatment of FL/DLBCL.

CASE PRESENTATION

This is a 43-year-old Chinese man who was diagnosed with low grade FL (account for 80%) combined with DLBCL (20%) at a stage of IVB. The patient presented with BCL2/IGH translocation without MYC rearrangement, as well as the expressions of CD20, CD19, CD10 and BCL2 at the initial diagnosis of FL/DLBCL. MYC rearrangement and TdT expression occurred after the treatment. The targeted sequencing revealed mutations in KMT2D, FOXO1, CREBBP, ATM, STAT6, BCL7A, DDX3X, MUC4, FGFR3, ARID5B, DDX11 and PRKCSH genes were the co-mutations shared by the FL/DLBCL and TdT positive "double hit" HGBL, while CCND3, BIRC6, ROBO1 and CHEK2 mutations specifically occurred after the treatment. The overall survival time was 37.8 and 17.8 months after the initial diagnosis of FL/DLBCL and TdT positive "double hit" HGBL, respectively.

CONCLUSION

This study reports a rare case of TdT positive "double hit" HGBL following the treatment of concurrent FL/DLBCL and highlights the mutation characteristics. Collectively, this study will help enrich the knowledge of TdT positive "double hit" HGBL transformed from FL/DLBCL.

Fifth Edition of the World Health Classification of Tumors of the Hematopoietic and Lymphoid Tissues: B-cell Neoplasms

We review B-cell neoplasms in the 5th edition of the World Health Organization classification of hematolymphoid tumors (WHO-HEM5). The revised classification is based on a multidisciplinary approach including input from pathologists, clinicians, and other experts. The WHO-HEM5 follows a hierarchical structure allowing the use of family (class)-level definitions when defining diagnostic criteria are partially met or a complete investigational workup is not possible. Disease types and subtypes have expanded compared with the WHO revised 4th edition (WHO-HEM4R), mainly because of the expansion in genomic knowledge of these diseases. In this review, we focus on highlighting changes and updates in the classification of B-cell lymphomas, providing a comparison with WHO-HEM4R, and offering guidance on how the new classification can be applied to the diagnosis of B-cell lymphomas in routine practice.

Aggressive B-cell non-Hodgkin lymphomas: a report of the lymphoma workshop of the 20th meeting of the European Association for Haematopathology

Aggressive B-cell non-Hodgkin lymphomas are a heterogeneous group of diseases and our concepts are evolving as we learn more about their clinical, pathologic, molecular genetic features. Session IV of the 2020 EAHP Workshop covered aggressive, predominantly high-grade B-cell lymphomas, many that were difficult to classify. In this manuscript, we summarize the features of the submitted cases and highlight differential diagnostic difficulties. We specifically review issues related to high-grade B-cell lymphomas (HGBCLs) with MYC and BCL2 and/or BCL6 rearrangements including TdT expression in these cases, HGBCL, not otherwise specified, large B-cell lymphomas with IRF4 rearrangement, high-grade/large B-cell lymphomas with 11q aberration, Burkitt lymphoma, and pleomorphic mantle cell lymphoma. Since the workshop, the 5th edition of the WHO Classification for Haematolymphoid Tumours (WHO-HAEM5) and International Consensus Classification (ICC) 2022 were published. We endeavor to use the updated terminology.

The Clinicopathologic Features and Molecular Signatures of Blastoid High-Grade B Cell Lymphoma, Not Otherwise Specified

A small subset of high-grade B-cell lymphoma (HGBL) with blastoid morphology remains poorly understood. We assessed 55 cases of blastoid HGBL, not otherwise specified (NOS) and compared their clinicopathologic characteristics with those of 81 non-blastoid HGBL-NOS and 62 blastoid HGBL with MYC and BCL2, with or without BCL6 rearrangements (double/triple-hit lymphoma [D/THL]). Patients with blastoid HGBL-NOS showed similar clinicopathologic features to patients with blastoid D/THLs and non-blastoid HGBL-NOS, except more frequently with a history of low-grade B-cell lymphoma, bone marrow involvement, and BCL2 rearrangement (P < .05) compared to the latter. MYC rearrangement (MYC-R), detected in 40% of blastoid HGBL-NOS, was associated with aggressive clinicopathologic features and poorer overall survival, even worse than that of blastoid D/THL (P < .05). Transcriptome profiling revealed a distinct gene expression pattern with differentially expressed genes enriched in MYC and P53-targeted genes in MYC-R blastoid HGBL-NOS. Fifty-two percent of blastoid HGBL-NOS had a double hit-like signature, similar to non-blastoid HGBL-NOS (P = .73). The overall survival of the blastoid HGBL-NOS group was similar to that of the blastoid D/THL group but appeared poorer than that of its non-blastoid counterparts (P = .07). Taken together, blastoid HGBL-NOS is an aggressive B-cell lymphoma that shares overlapping clinicopathologic and genetic features with non-blastoid HGBL-NOS. MYC-R in patients with blastoid HGBL-NOS identifies a highly aggressive subgroup with distinct aggressive clinicopathologic features, unique molecular signatures, and a dismal clinical outcome.

Progression of follicular lymphoma and related entities: Report from the 2021 SH/EAHP Workshop

OBJECTIVES

The 2021 Society for Hematopathology and European Association for Haematopathology Workshop addressed the molecular and cytogenetic underpinnings of transformation and transdifferentiation in lymphoid neoplasms.

METHODS

Session 4, "Transformations of Follicular Lymphoma," and session 5, "Transformations of Other B-Cell Lymphomas," included 45 cases. Gene alteration analysis and expression profiling were performed on cases with submitted formalin-fixed, paraffin embedded tissue.

RESULTS

The findings from session 4 suggest that "diffuse large B-cell lymphoma/high-grade B-cell lymphoma with rearrangements of MYC and BCL2" is a distinct category arising from the constraints of a preexisting BCL2 translocation. TdT expression in aggressive B-cell lymphomas is associated with MYC rearrangements, immunophenotypic immaturity, and a dismal prognosis but must be differentiated from lymphoblastic -lymphoma. Cases in session 5 illustrated unusual morphologic and immunophenotypic patterns of transformation. Additionally, the findings support the role of cytogenetic abnormalities-specifically, MYC and NOTCH1 rearrangements-as well as single gene alterations, including TP53, in transformation.

CONCLUSIONS

Together, these unique cases and their accompanying molecular and cytogenetic data suggest potential mechanisms for and unusual patterns of transformation in B-cell lymphomas and indicate numerous opportunities for further study.

Modern Classification and Management of Pediatric B-cell Leukemia and Lymphoma

Although pediatric hematopathology overlaps with that of adults, certain forms of leukemia and lymphoma, and many types of reactive conditions affecting the bone marrow and lymph nodes, are unique to children. As part of this series focused on lymphomas, this article (1) details the novel subtypes of lymphoblastic leukemia seen primarily in children and described since the 2017 World Health Organization classification and (2) discusses unique concepts in pediatric hematopathology, including nomenclature changes and evaluation of surgical margins in selected lymphomas.

High-grade B-cell lymphoma (HGBL)-NOS is clinicopathologically and genetically more similar to DLBCL/HGBL-DH than DLBCL

High-grade B-cell lymphoma, not otherwise specified (HGBL-NOS) is rare and data focused on these neoplasms is lacking. We studied the clinicopathologic and genetic features of 136 HGBL-NOS patients and compared them to patients with DLBCL/HGBL-DH (n = 224, defined by 5th Edition WHO) and DLBCL (n = 217). HGBL-NOS patients had clinical features similar to DLBCL/HGBL-DH patients. MYC rearrangement (MYC-R) was present in 43% of HGBL-NOS. With induction regimen similar to DLBCL/HGBL-DH patients, HGBL-NOS patients had a median overall survival (OS) of 28.9 months, similar to DLBCL/HGBL-DH (p = 0.48) but inferior to DLBCL patients (p = 0.03). R-EPOCH induction was associated with improved OS compared with R-CHOP. MYC-R, history of lymphoma, and high IPI were independent adverse prognostic factors in HGBL-NOS patients. Whole transcriptome profiling performed on a subset of HGBL-NOS cases showed a profile more similar to DLBCL/HGBL-DH than to DLBCL; 53% of HGBL-NOS had a DH-like signature (DH-like-Sig) and were enriched for MYC-R. DH-like-Sig+ HGBL-NOS patients had a poorer OS than DH-like-Sig-negative patients (p = 0.04). In conclusion, HGBL-NOS has clinicopathologic features and a gene expression profile more similar to DLBCL/HGBL-DH than to DLBCL. Cases of HGBL-NOS frequently carry MYC-R and have a DH-like-Sig+. R-EPOCH induction in HGBL-NOS appears associated with improved OS compared with standard R-CHOP.

Blastoid B-Cell Neoplasms: Diagnostic Challenges and Solutions

Blastoid B-cell neoplasms mainly include B-lymphoblastic leukemia/lymphoma (B-ALL), blastoid mantle cell lymphoma, and high-grade B-cell lymphoma with blastoid morphologic features (blastoid HGBL). Distinguishing blastoid HGBL from B-ALL can be challenging and we previously developed six-point flow cytometry-focused and three-point immunohistochemistry-focused scoring systems to aid in differential diagnosis. However, the six-point scoring system was derived from bone marrow cases and occasional cases may have a misleading score using either system. In this study, we assessed 121 cases of blastoid-HGBL (37 BM and 84 extramedullary) to validate the six-point scoring system in all tissue types and to further compare the two scoring systems. Compared with 47 B-ALL cases enriched for CD34-negative neoplasm, the 121 blastoid-HGBL cases showed distinctive pathologic features. The six-point scoring system showed a sensitivity of 100%. A comparison of the two scoring systems in blastoid HGBL (n = 64) and B-ALL (n = 37) showed a concordance score rate of 88%. Thirteen cases showed misleading scores, including five HGBL and eight B-ALL, and the diagnosis was further validated by gene transcriptome profiling. Twelve of thirteen cases had discordant scores between the two scoring systems. Simultaneous employment of both scoring systems improved the accuracy of classification of blastoid B-cell neoplasms to 99%. In conclusion, the previously defined six-point scoring system showed an excellent performance regardless of the tissue origin. Using both scoring systems together improves the accuracy of classification of blastoid B-cell neoplasms. Cases with discordant scores between the two scoring systems were extremely challenging neoplasms and classification required correlation with all available clinical and genetic features.

International Consensus Classification of acute lymphoblastic leukemia/lymphoma

The updated International Consensus Classification (ICC) of B-acute lymphoblastic leukemia (B-ALL) and T-acute lymphoblastic leukemia (T-ALL) includes both revisions to subtypes previously outlined in the 2016 WHO classification and several newly described entities. The ICC classification incorporates recent clinical, cytogenetic, and molecular data, with a particular emphasis on whole transcriptome analysis and gene expression (GEX) clustering studies. B-ALL classification is modified to further subclassify BCR::ABL1-positive B-ALL and hypodiploid B-ALL. Additionally, nine new categories of B-ALL are defined, including seven that contain distinguishing gene rearrangements, as well as two new categories that are characterized by a specific single gene mutation. Four provisional entities are also included in the updated B-ALL classification, although definitive identification of these subtypes requires GEX studies. T-ALL classification is also updated to incorporate BCL11B-activating rearrangements into early T-precursor (ETP) ALL taxonomy. Additionally, eight new provisional entities are added to the T-ALL subclassification. The clinical implications of the new entities are discussed, as are practical approaches to the use of different technologies in diagnosis. The enhanced specificity of the new classification will allow for improved risk stratification and optimized treatment plans for patients with ALL.

Diagnostic approaches and future directions in Burkitt lymphoma and high-grade B-cell lymphoma

Since the 2016 WHO update, progress has been made in understanding the biology of Burkitt lymphoma (BL) and the concept of high-grade B-cell lymphomas (HGBCL) that allows some degree of refinement. The summary presented here reviews in detail the discussions of the Clinical Advisory Committee and expands upon the newly published 2022 International Consensus Classification for lymphoid malignancies (Campo et al. Blood, 2022). BL remains the prototypic HGBCL and diagnostic criteria are largely unchanged. HGBCL with MYC and BCL2 and HGBCL with MYC and BCL6 rearrangements are now separated to reflect biologic and pathologic differences. HGBCL, NOS remains a diagnosis of exclusion that should be used only in rare cases. FISH strategies for diffuse large B-cell lymphoma (DLBCL) and HGBCL are discussed in detail for these diseases. Advances in integrative analysis of mutations, structural abnormalities, copy number, and gene expression signatures allow a more nuanced view of the heterogeneity of DLBCL, NOS as well as definitions of HGBCL and point to where the future may be headed for classification of these diseases.

Blastoid high-grade B-cell lymphoma initially presenting in bone marrow: a diagnostic challenge

The 2016 WHO classification introduced the category of high-grade B-cell lymphoma (HGBL), which includes one poorly understood subset, blastoid-HGBL. Establishing the diagnosis and distinguishing blastoid-HGBL from B-acute lymphoblastic leukemia (B-ALL) in bone marrow can be challenging. We assessed 31 cases of blastoid-HGBL diagnosed initially in bone marrow and compared this group to 36 cases of B-ALL using immunophenotyping, fluorescence in situ hybridization, and targeted next generation sequencing analysis. The 31 blastoid-HGBL cases included 14 HGBL with MYC and BCL2 and/or BCL6 rearrangements (double hit lymphoma, DHL), 13 HGBL, not otherwise specified (NOS), and four cases with TdT expression that were difficult to classify. Compared with B-ALL, blastoid-HGBL cases more often showed increased intensity/bright expression of CD20, CD38, CD45, BCL-6, and MYC, and less frequent bright expression of CD10 and TdT. Cases of blastoid-HGBL also more frequently had MYC rearrangement, a complex karyotype and TP53 mutation (p < 0.01). With the exception of CD34, no other single factor, including TdT, was sensitive or adequately specific to distinguish blastoid-HGBL from B-ALL. We developed a scoring system using six distinctive features between 16 cases of unequivocal blastoid HGBL and 22 cases of CD34-positive B-ALL, with a score of ≥3 defining blastoid-HGBL. The system was further validated by using 15 cases of surface light chain negative, and/or CD45 dim to negative blastoid-HGBL and 14 cases of CD34-negative B-ALL. The sensitivity, specificity, positive, and negative predictive value of this scoring system were 100%, 94%, 94%, and 100%, respectively. Using this system, the four cases with TdT expression were all classified as blastoid-HGBL: three were DHL and one was HGBL-NOS. In conclusion, blastoid-HGBL shows distinctive immunophenotypic, cytogenetic, and molecular features as compared with B-ALL. The proposed scoring system can be helpful for the classification of diagnostically challenging blastoid lymphoid tumors presenting initially in the bone marrow.

A comparison of capillary electrophoresis and next-generation sequencing in the detection of immunoglobulin heavy chain H and light chain κ gene rearrangements in the diagnosis of classic hodgkin’s lymphoma

This study aimed to compare the application value of capillary electrophoresis and next-generation sequencing for immunoglobulin (IG) gene rearrangement in the diagnosis of classic Hodgkin’s lymphoma. Twenty paraffin-embedded specimens from patients with classic Hodgkin’s lymphoma were screened. For gene rearrangement detection, the ABI 3500 Genetic Analyzer and ABI Ion GeneStudio S5 Plus sequencing system were used, respectively, and the results were compared. Five cases with monoclonal rearrangements (25%, 5/20) were detected by Capillary Electrophoresis, and positivity for the FR1, FR2, FR3, and IGк loci was 5%, 10%, 10%, and 15%, respectively; 12 cases with monoclonal rearrangements (60%, 12/20) were detected by Next-generation Sequencing where the positivity of the above corresponding loci were 35%, 45%, 50%, and 30%, respectively. Among the 20 samples, 6 IGк clonal rearrangements were detected, and the usage frequency (66.7%) of IGкJ4 was the highest in the IGкJ subgroup. The usage frequency of IGкV1 and IGкV3 in the GкV sub-group was 33.3% and 33.3%, respectively. Twelve immunoglobulin heavy chain (IGH) clonal rearrangements were detected among the 20 samples, and the order of usage frequency in the IGH joining region J (IGHJ) subgroup was IGHJ4 > IGHJ5 > IGHJ6 > IGHJ3. The gene with the highest usage frequency in the IGH variable (IGHV) subgroup was IGHV3 (50%) and the percentage of IGHV mutations ranged from 0% ± 11.45% with an average frequency of 3.34%. Compared with Capillary Electrophoresis, Next-generation Sequencing showed a higher positivity in the detection of gene clonal rearrangements, was more accurate in the interpretation of results.

Identification of DNA Damage Repair-Associated Prognostic Biomarkers for Prostate Cancer Using Transcriptomic Data Analysis

In the recent decade, the importance of DNA damage repair (DDR) and its clinical application have been firmly recognized in prostate cancer (PC). For example, olaparib was just approved in May 2020 to treat metastatic castration-resistant PC with homologous recombination repair-mutated genes; however, not all patients can benefit from olaparib, and the treatment response depends on patient-specific mutations. This highlights the need to understand the detailed DDR biology further and develop DDR-based biomarkers. In this study, we establish a four-gene panel of which the expression is significantly associated with overall survival (OS) and progression-free survival (PFS) in PC patients from the TCGA-PRAD database. This panel includes DNTT, EXO1, NEIL3, and EME2 genes. Patients with higher expression of the four identified genes have significantly worse OS and PFS. This significance also exists in a multivariate Cox regression model adjusting for age, PSA, TNM stages, and Gleason scores. Moreover, the expression of the four-gene panel is highly correlated with aggressiveness based on well-known PAM50 and PCS subtyping classifiers. Using publicly available databases, we successfully validate the four-gene panel as having the potential to serve as a prognostic and predictive biomarker for PC specifically based on DDR biology.

EBV-positive high-grade B-cell lymphoma with MYC and BCL2 and/or BCL6 rearrangements: a multi-institutional study

AIMS

It is unknown whether Epstein-Barr virus (EBV) infection can occur in high-grade B-cell lymphoma with MYC and BCL2 and/or BCL6 rearrangements, also known as double-hit or triple-hit lymphoma (DHL/THL).

METHODS AND RESULTS

Here we report 16 cases of EBV+ DHL/THL from screening 846 cases of DHL/THL and obtaining additional EBV+ cases through multi-institutional collaboration: 8 MYC/BCL2 DHL, 6 MYC/BCL6 DHL, and 2 THL. There were 8 men and 8 women with a median age of 65 years (range, 32-86). Two patients had a history of follicular lymphoma and one had AIDS. Nine of 14 patients had an International Prognostic Index of ≥3. Half of the cases showed high-grade/Burkitt-like morphology and the other half diffuse large B-cell lymphoma morphology. By immunohistochemistry, the lymphoma cells were positive for MYC (n=14/16), BCL2 (n=12/16), BCL6 (n=14/16), CD10 (n=13/16), and MUM1 (n=6/14). By Hans algorithm, 13 cases were classified as GCB and 3 as non-GCB. The lymphomas frequently showed an EBV latency type I with a median EBV-encoded small RNAs of 80% positive cells (range, 20-100%). After a median follow-up of 36.3 months (range, 2.0-41.6), 7 patients died with a median survival of 15.4 months (range, 3.4-47.3) after diagnosis of EBV+ DHL/THL. Five of 6 patients with MYC/BCL6 DHL were alive including 4 in complete remission. In contrast, only 4/10 patients with MYC/BCL2 DHL or THL were alive including 2 in complete remission. The median survival in patients with MYC/BCL6 DHL was unreached and was 21.6 months in patients with MYC/BCL2 DHL or THL.

CONCLUSIONS

EBV infection in DHL/THL is rare (~1.5%). Cases of EBV+ DHL/THL are largely similar to their EBV-negative counterparts clinicopathologically. Our findings expand the spectrum of EBV+ B-cell lymphomas currently recognized in the WHO classification and suggest differences between EBV+ MYC/BCL2 and MYC/BCL6 DHL that may have therapeutic implications.

Mutational Landscape of TdT+ Large B-cell Lymphomas Supports Their Distinction From B-lymphoblastic Neoplasms: A Multiparameter Study of a Rare and Aggressive Entity

In the current World Health Organization classification, terminal deoxynucleotidyl transferase (TdT) expression in a high grade/large cell B-cell lymphoma (LBCL) indicates a B-lymphoblastic lymphoma/leukemia (B-LBL), although TdT expression in what appear to be mature LBCL or following mature B-cell neoplasms is reported. The frequency of TdT+ LBCL, how to best categorize these cases, and their clinicopathologic features, molecular landscape, and relationship to classic B-LBL remain to be better defined. TdT expression was therefore assessed in 258 LBCL and the results correlated with the cytologic, phenotypic, and cytogenetic findings. Targeted mutational analysis, review of prior biopsies, and assessment of clinical associations was performed in the 6 cases with >10% TdT+ cells. All 6 TdT+ LBCL were blastoid-appearing, CD34-, MYC+, BCL2+, and had MYC rearrangements (R) (5/6 with BCL2 and/or BCL6-R). 5/6 had a prior TdT- LBCL and/or follicular lymphoma and all had an aggressive course. Fifteen nonsynonymous variants in 11 genes were seen in the 4/5 tested cases with mutations. TdT+ and TdT- areas in 1 case showed identical mutations. The mutational profiles were more like those reported in germinal center B-cell type-diffuse LBCL rather than B-LBL. Evolution from preceding TdT- lymphomas was nondivergent in 1/3 tested cases and partially divergent in 2. The clinicopathologic and cytogenetic features of these 6 cases were similar to those found in a meta-analysis that included additional cases of TdT+ LBCL or B-LBL following follicular lymphoma. Thus, TdT+, CD34- large B-cell neoplasms with MYC rearrangements and often a "double hit" are rare, frequently a transformational event and aggressive but are distinct from classic B-LBL.

ERG Immunoreactivity in Blastic Hematolymphoid Neoplasms: Diagnostic Pitfall in the Workup of Undifferentiated Malignant Neoplasms

Undifferentiated malignant neoplasms pose diagnostic challenges, and reliable immunohistochemical markers with well-characterized staining profiles are desirable when characterizing them. Our initial observation of erythroblast transformation specific regulated gene-1 (ERG) reactivity in myeloid sarcomas led us to broadly explore the utility of ERG as a marker of immature hematolymphoid neoplasms presenting in extramedullary sites. We stained 207 immature and mature hematolymphoid lesions as well as 39 benign hematolymphoid tissues and found weak-to-moderate ERG immunopositivity in 15 of 16 (94%) acute myeloid leukemias/myeloid sarcomas, including 4 of 5 (80%) CD34-negative/CD117-negative acute myeloid leukemias/myeloid sarcomas. ERG positivity was also seen in all 9 cases of B-lymphoblastic and T-lymphoblastic leukemia/lymphoma, all 3 cases of hematogone hyperplasia, and all 4 cases of systemic mastocytosis. ERG was negative in 148 mature B-cell and T-cell lymphomas, including 2 high-grade B-cell lymphomas and 2 blastoid variant mantle cell lymphomas; 23 histiocytic/dendritic cell neoplasms; 2 indolent T-lymphoblastic proliferations; and 2 blastic plasmacytoid dendritic cell neoplasms. We conclude that ERG immunoreactivity may pose a significant diagnostic pitfall in the workup of undifferentiated malignant neoplasms, particularly those presenting in extramedullary sites.

De novo double-hit B-cell precursor leukemia/lymphoma - an unusual presentation as peritoneal lymphomatosis

Peritoneal lymphomatosis (PL) is a rare presentation of extranodal precursor leukemia/lymphoma. The presentation is often non-specific, leading to delayed diagnosis and treatment. In this case, though the preliminary diagnosis was established on ascitic fluid cytology, the disease progressed rapidly, leading to demise before initiating chemotherapy. Immunophenotyping and molecular studies, performed later, established a diagnosis of de novo B-cell precursor leukemia/lymphoma with MYC, BCL2 rearrangements (Double-hit lymphoma). MYC, BCL2 rearrangements are rarely reported in precursor B-lymphoma/leukemia which carry dismal prognosis. In this report, we illustrate autopsy findings of PL in an elderly gentleman who presented with ascites for evaluation.

Relative frequency and clinicopathologic characteristics of MYC-rearranged follicular lymphoma

MYC rearrangement is a relatively rare genetic abnormality in follicular lymphoma (FL). In this study, we evaluated the relative frequency of MYC rearrangement in 522 cases of FL and studied their clinicopathologic, cytogenetic, and molecular characteristics. Fluorescence in situ hybridization studies for MYC (break-apart probe), MYC/IGH, IGH/BCL2, and BCL6 rearrangements were performed on tissue microarrays. Immunohistochemical stains for CD10, BCL2, BCL6, and MYC were performed and scored on MYC-rearranged cases. On 4 FL cases, a custom targeted panel of 356 genes was used for mutation analysis. Ten cases (1.9%) were positive for MYC rearrangement. Histologically, 6 of 10 cases were grade 1-2, and 4 cases were grade 3A. By immunohistochemistry, 9 of 9 tested cases were CD10+, all cases were BCL6+, and 9/10 cases were BCL2+. MYC protein staining was low in all cases tested. IGH/BCL2 rearrangement was detected in 5 of 9 cases, whereas BCL6 rearrangement was detected in 3 of 7 tested cases and 4 of 10 cases showed MYC/IGH rearrangement. The most commonly detected mutations in the MYC-positive cases included HLA-B, TNFRSF14, and KMT2D. MYC and/or B2M abnormalities were detected in 2 cases. In conclusion, MYC rearrangement is uncommon in FL and these cases do not appear to have specific histologic characteristics. Molecular analysis showed abnormalities in genes associated with transformation, namely MYC and B2M. Larger studies are needed to evaluate if MYC-rearrangement in FL has prognostic significance.

New developments in non-Hodgkin lymphoid malignancies

The revised fourth edition of the World Health Organization (WHO) Classification of Tumours of Haematopoietic and Lymphoid Tissues (2017) reflects significant advances in understanding the biology, genetic basis and behaviour of haematopoietic neoplasms. This review focuses on some of the major changes in B-cell and T-cell non-Hodgkin lymphomas in the 2017 WHO and includes more recent updates. The 2017 WHO saw a shift towards conservatism in the classification of precursor lesions of small B-cell lymphomas such as monoclonal B-cell lymphocytosis, in situ follicular and in situ mantle cell neoplasms. With more widespread use of next generation sequencing (NGS), special entities within follicular lymphoma and mantle cell lymphoma were recognised with recurrent genetic aberrations and unique clinicopathological features. The diagnostic workup of lymphoplasmacytic lymphoma and hairy cell leukaemia has been refined with the discovery of MYD88 L265P and BRAF V600E mutations, respectively, in these entities. Recommendations in the immunohistochemical evaluation of diffuse large B-cell lymphoma include determining cell of origin and expression of MYC and BCL2, so called 'double-expressor' phenotype. EBV-positive large B-cell lymphoma of the elderly has been renamed to recognise its occurrence amongst a wider age group. EBV-positive mucocutaneous ulcer is a newly recognised entity with indolent clinical behaviour that occurs in the setting of immunosuppression. Two lymphomas with recurrent genetic aberrations are newly included provisional entities: Burkitt-like lymphoma with 11q aberration and large B-cell lymphoma with IRF4 rearrangement. Aggressive B-cell lymphomas with MYC, BCL2 and/or BCL6 rearrangements, so called 'double-hit/triple-hit' lymphomas are now a distinct entity. Much progress has been made in understanding intestinal T-cell lymphomas. Enteropathy-associated T-cell lymphoma, type II, is now known to not be associated with coeliac disease and is hence renamed monomorphic epitheliotropic T-cell lymphoma. An indolent clonal T-cell lymphoproliferative disorder of the GI tract is a newly included provisional entity. Angioimmunoblastic T-cell lymphoma and nodal T-cell lymphomas with T-follicular helper phenotype are included in a single broad category, emphasising their shared genetic and phenotypic features. Anaplastic large cell lymphoma, ALK- is upgraded to a definitive entity with subsets carrying recurrent rearrangements in DUSP22 or TP63. Breast implant-associated anaplastic large cell lymphoma is a new provisional entity with indolent behaviour. Finally, cutaneous T-cell proliferations include a new provisional entity, primary cutaneous acral CD8-positive T-cell lymphoma, and reclassification of primary small/medium CD4-positive T-cell lymphoma as lymphoproliferative disorder.

Mantle cell lymphomas with concomitant MYC and CCND1 breakpoints are recurrently TdT positive and frequently show high-grade pathological and genetic features

Chromosomal breakpoints involving the MYC gene locus, frequently referred to as MYC rearrangements (MYC - R+), are a diagnostic hallmark of Burkitt lymphoma and recurrent in many other subtypes of B-cell lymphomas including follicular lymphoma, diffuse large B-cell lymphoma and other high-grade B-cell lymphomas and are associated with an aggressive clinical course. In remarkable contrast, in MCL, only few MYC - R+ cases have yet been described. In the current study, we have retrospectively analysed 16 samples (MYC - R+, n = 15, MYC - R-, n = 1) from 13 patients and describe their morphological, immunophenotypic and (molecular) genetic features and clonal evolution patterns. Thirteen out of fifteen MYC - R+ samples showed a non-classical cytology including pleomorphic (centroblastic, immunoblastic), anaplastic or blastoid. MYC translocation partners were IG-loci in 4/11 and non-IG loci in 7/11 analysed cases. The involved IG-loci included IGH in 3 cases and IGL in one case. PAX5 was the non-IG partner in 2/7 patients. The MYC - R+ MCL reported herein frequently displayed characteristics associated with an aggressive clinical course including high genomic-complexity (6/7 samples), frequent deletions involving the CDKN2A locus (7/10 samples), high Ki-67 proliferation index (12/13 samples) and frequent P53 expression (13/13 samples). Of note, in 4/14 samples, SOX11 was not or only focally expressed and 3/13 samples showed focal or diffuse TdT-positivity presenting a diagnostic challenge as these features could point to a differential diagnosis of diffuse large B-cell lymphoma and/or lymphoblastic lymphoma/leukaemia.

Aggressive B-cell lymphomas with a primary bone marrow presentation

Aggressive B-cell lymphomas present as a heterogeneous spectrum of disease. A primary diagnosis in the bone marrow (BM) may be challenging in terms of diagnostic classification and clinical handling, owing to limited architectural information. Aggressive B-cell lymphomas can be subdivided into entities that typically present primarily in the BM, and cases with BM involvement in which the bulk of disease is present in other organs. One main topic at the 2018 BM workshop of the European Association of Haematopathology/Society of Hematopathology was therefore aggressive B-cell lymphomas with a primary BM presentation. The spectrum of cases submitted to this topic gave a good overview of commonly encountered problems, as well as unusual manifestations, and highlighted areas of imprecise disease definitions and diagnostic grey zones. The categories submitted to the workshop included cases of Burkitt lymphoma (BL) with unusual features, high-grade B-cell lymphomas (HG-BCLs) with and without so-called double/triple-hit, and diffuse large B-cell lymphomas (DLBCLs) with a primary BM presentation. Areas of difficulties included the morphological boundaries of HG-BCL not otherwise specified, cases with MYC and bcl-2 or bcl-6 translocations and terminal deoxynucleotidyl transferase (TdT) expression, which were categorised as B-cell lymphoblastic leukaemia/lymphoma if most cells showed TdT positivity, and the clinicopathological overlap between intravascular large B-cell lymphoma, CD5-positive DLBCL, and DLBCL with primary presentations in the BM, spleen, and liver. This review summarises our understanding of the main aggressive B-cell lymphoma categories with a common primary BM presentation and potential problem areas, and makes suggestions for the immunophenotypic and genetic work-up, illustrated by the interesting and challenging cases submitted to the workshop.

Non-diffuse large B-cell lymphoma transformation from follicular lymphoma: a single-institution study of 19 cases

Diffuse large B-cell lymphoma (DLBCL) is the most common histological transformation (HT) of follicular lymphoma (FL). Other types of HT are very rare, and their incidence, histopathology, and patient outcomes have not been sufficiently described. Here, we assessed the clinicopathological characteristics of 19 cases of non-DLBCL HT of FL in a single institution in Japan to advance the understanding of the disease. Among 889 consecutive patients diagnosed with FL between 2000 and 2018, 191 suffered HT (21%). The median follow-up period was 94 months (range = 3-225). A total of 172 patients (90%) had DLBCL transformation, whereas the remaining 19 patients (10%) exhibited non-DLBCL transformation. In the latter cases, the following diagnoses were made based on morphology, immunohistochemistry, flow cytometry, and fluorescence in situ hybridization analyses: classic Hodgkin lymphoma (7 patients; 4%); high-grade B-cell lymphoma (HGBL) with MYC and BCL2 rearrangements (4 patients; 2%); HGBL, not otherwise specified (4 patients; 2%); B-cell lymphoblastic leukemia/lymphoma (2 patients; 1%); anaplastic large-cell lymphoma-like lymphoma (1 patient; 0.5%); and plasmablastic lymphoma (1 patient; 0.5%). Epstein-Barr virus-encoded RNA-1 did not associate with HT in any of the cases tested (n = 8). Patients with non-DLBCL transformation showed poor outcomes, with a median overall survival of 13 months (range = 2 days-107 months); 10 of the patients (53%) died of HT. In conclusions, non-DLBCL transformation was observed in 10% of patients with HT from FL. Our data show that timely, accurate, and comprehensive histopathological diagnosis is needed to ensure optimal treatment and improve the outcome of these patients.

Dramatic increase in gene mutational burden after transformation of follicular lymphoma into TdT+ B-lymphoblastic leukemia/lymphoma

Transformation of follicular lymphoma (FL) into B-lymphoblastic leukemia/lymphoma (B-ALL/LBL) is rare and results in greatly increased aggressiveness of clinical course. Here we present extensive molecular analysis of this unusual transformation, including immunoglobulin (Ig) gene rearrangement studies, cytogenetic analysis, and whole-exome sequencing (WES) of the patient's FL, B-ALL/LBL, and normal cells. Although FL showed marked somatic hypermutation (SHM) of the Ig genes, SHM appeared to be even more extensive in B-ALL/LBL. Cytogenetically, at least three translocations were identified in the B-ALL/LBL involving the BCL2, BCL6, and MYC genes; two of these, the BCL6 and BCL2 gene rearrangements, were already seen at the FL stage. WES identified 751 single-nucleotide variants with high allelic burden in the patient's cells, with the vast majority (575) present exclusively at the B-ALL/LBL stage. Of note, a TAF3 gene mutation was shared by normal, FL, and B-ALL/LBL tissue. A KMT2D nonsense mutation was identified in both FL and B-ALL/LBL and therefore may have contributed directly to lymphomagenesis. Mutations in KDM6A, SMARCA4, CBX1, and JMY were specific to the B-ALL/LBL stage, possibly contributing to the B-ALL/LBL transformation. Functionally, these identified mutations may lead to dysregulation of DNA repair, transcription, and cell differentiation. Thus, these genetic changes, together with the identified chromosomal translocations, may have contributed to lymphoma development and progression. Our findings may improve the mechanistic understanding of the FL-B-ALL/LBL transformation and may have therapeutic implications for this aggressive disease.

Molecular characteristics of terminal deoxynucleotidyl transferase negative precursor B-cell phenotype Burkitt leukemia with IGH-MYC rearrangement

Precursor B cell phenotype Burkitt lymphoma/leukemia with IGH-MYC is a rare subtype of Burkitt lymphoma (BL). BL and B lymphoblastic leukemia/lymphoma (B-ALL/LBL) differ as regards treatment and the distinction between these two entities is crucial. Patients demonstrating a terminal deoxynucleotidyl transferase (TdT)-positive precursor B cell phenotype with IGH-MYC rearrangement have been reported to be molecularly distinct from BL and closer to B-ALL/LBL. We investigated the molecular characteristics of two cases of a rare but distinct TdT-negative precursor B cell phenotype BL. Both patients showed FAB L3 morphology with IGH-MYC translocation, but had precursor B cell immunophenotypes including dim to moderate expression of CD45 and absence of BCL6, CD20, monoclonal kappa, and lambda light chain expression. To characterize the molecular features, we performed exome sequencing and analyzed the breakpoint junction of the IGH-MYC rearrangement. We detected KMT2D mutations in both cases, a rarely acquired chromatin modifying gene mutation in BL. The breakpoint analysis revealed that the IGH-MYC rearrangement occurred due to an aberrant VDJ recombination in one case. The treatment protocols differed, including high-grade lymphoma treatment and standard B-ALL treatment. Complete remission was achieved in the patient who received B-ALL treatment. The degree of resemblance of BL and B-ALL differed between two cases, but the molecular pathogenesis and manifesting features of both TdT-negative precursor B cell phenotype BL case were distinct from classic BL, which indicates the need for a better understanding of this uncommon entity that does not fit in current diagnostic and classification categories.

Double-hit pancreatic B-lymphoblastic lymphoma with a variant translocation t(2;18)(p11;q21)

Double-hit lymphoma is typically categorized as "high-grade B-cell lymphoma, with MYC and BCL2 and/or BCL6 rearrangements", but in infrequent cases in which terminal deoxynucleotidyl transferase (TdT) expression is positive, it is categorized as B-lymphoblastic lymphoma (B-LBL). BCL2 rearrangements are usually caused by t(14;18)(q32;q21); variant translocations are very rare. Here, we describe an unusual case of double-hit pancreatic B-LBL with a variant translocation t(2;18)(p11;q21). A 69-year-old man was admitted because of an abdominal mass. Computed tomography scans demonstrated a diffusely enlarged pancreas and massive ascites. Cell block preparations of ascites cells revealed marked proliferation of blastic lymphoid cells positive for CD19, CD10, CD79a, PAX5, and TdT, indicating a diagnosis of B-LBL. G-banding and spectral karyotyping showed 45,XY,+X,t(2;18)(p11;q21),-4,der(5)t(1;5)(q12;p15),der(6)t(6;21)(q21;q?),t(8;14)(q24;q32),-15. Fluorescence in situ hybridization detected split BCL2 and IGH/MYC fusion signals. Almost all ascites cells were diffusely and strongly positive for MYC and BCL2. The patient died of progressive disease 20 days after admission. To our knowledge, this is the first reported case of MYC and BCL2 double-hit B-LBL with t(2;18)(p11;q21). High coexpression of MYC by t(8;14) and BCL2 by t(2;18) may be implicated in the development of B-LBL. Furthermore, double-hit B-LBL may be associated with a less favorable outcome compared with typical B-LBL.