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Islands of CD123high cells have been commonly described in the bone marrow of patients with chronic myelomonocytic leukemia (CMML). Using a multiparameter flow cytometry assay, we detected an excess of CD123+ mononucleated cells that are lineage-negative, CD45+, CD11c−, CD33−, HLA-DR+, BDCA-2+, BDCA-4+ in the bone marrow of 32/159 (20%) patients. Conventional and electron microscopy, flow cytometry detection of cell surface markers, gene expression analyses, and the ability to synthesize interferon alpha in response to Toll-like receptor agonists identified these cells as bona fide plasmacytoid dendritic cells (pDCs). Whole-exome sequencing of sorted monocytes and pDCs identified somatic mutations in genes of the oncogenic RAS pathway in the two cell types of every patient. CD34+ cells could generate high amount of pDCs in the absence of FMS-like tyrosine kinase 3-ligand (FLT3L). Finally, an excess of pDCs correlates with regulatory T cell accumulation and an increased risk of acute leukemia transformation. These results demonstrate the FLT3L-independent accumulation of clonal pDCs in the bone marrow of CMML patients with mutations affecting the RAS pathway, which is associated with a higher risk of disease progression.

Abstract Primary leptomeningeal lymphoma is exceedingly rare. We describe 2 rare lymphoma cases with exclusive leptomeningeal disease: 1 ALK-positive (ALK+) anaplastic large cell lymphoma (ALCL) and 1 primary effusion lymphoma (PEL). Case 1: A 19-year-old man presented with symptoms concerning for leptomeningitis. Cerebrospinal fluid (CSF) analysis revealed lymphocytic pleocytosis. Spine MRI demonstrated pial enhancement from T10 through the conus medullaris and cauda equina enhancement/thickening. A biopsy showed leptomeningeal involvement by large lymphoma cells with hallmark cells and brisk mitotic activity. By immunohistochemistry, cells were CD7/CD30-positive with cytoplasmic ALK staining. No systemic disease was identified. The diagnosis of primary leptomeningeal ALK+ ALCL was made. Despite 2 CSF relapses requiring systemic therapy and autologous bone marrow transplant, the patient was in complete clinical remission 9 years after the diagnosis. Case 2: A 60-year-old, human immunodeficiency virus-positive man presented with symptoms suggestive of leptomeningitis. Brain MRIs revealed multifocal, supratentorial, and infratentorial leptomeningeal enhancement. A right frontal biopsy demonstrated leptomeningeal involvement by large lymphoma cells negative for B-cell immunostains, but CD138, MUM-1, and HHV8-positive, with aberrant CD3 expression. EBV-encoded RNA in situ hybridization was positive. In absence of solid lesions/extracranial involvement, the diagnosis of leptomeningeal PEL was rendered. Despite initial complete remission after chemotherapy, the patient died 9 months later.

Oncogene expression can cause replication stress (RS), leading to DNA double-strand breaks (DSBs) that require repair through pathways such as homologous recombination, nonhomologous end-joining, and microhomology-mediated end-joining (MMEJ). Cyclin D1 (encoded by CCND1) is a well-known oncoprotein overexpressed in cancer; however, its role in RS is unknown. Using mantle cell lymphoma (MCL) as a naturally occurring model of cyclin D1 overexpression, we examined the impact of cyclin D1 on RS and DSB repair mechanisms. Cyclin D1 overexpression elevated RS, increased DNA damage, especially during mitosis, and caused specific upregulation of MMEJ. Furthermore, cyclin D1 activated polymerase theta (POLQ) transcription by binding its promoter loci, driving POLΘ-mediated MMEJ that is essential to withstand cyclin D1-induced RS. Moreover, concurrent ATM deficiency further intensified RS, enhanced POLQ expression, and heightened reliance on MMEJ-mediated DNA damage repair. Consequently, inhibition of POLΘ in cyclin D1-overexpressed settings further exacerbated RS, causing single-strand DNA gap accumulations and chromosomal instability, ultimately leading to apoptosis, an effect amplified in ATM-deficient cells. Targeting MMEJ via POLΘ inhibition is therefore an effective strategy in the context of cyclin D1 overexpression and ATM deficiency and may provide a unique therapeutic approach for treating MCL and other malignancies characterized by similar alterations.

EBV-positive polymorphic B-cell lymphoproliferative disorder, NOS (poly B-LPD), is a newly defined entity in the 2022 International Consensus Classification of mature lymphoid neoplasms. Its clinical behavior and optimal treatment approach remain poorly characterized. We conducted a retrospective study of 31 patients diagnosed with EBV+ poly B-LPD at Mayo Clinic (2003–2024), excluding transplant recipients. Median age was 56 years; 71% had extranodal involvement, 68% presented with stage III/IV disease, and 52% had autoimmune conditions. Thirty-five percent ( n  = 11) were on immunosuppressive therapy at diagnosis, all of whom underwent reduction of immunosuppression (RIS); five underwent RIS alone, achieving four complete responses including two with central nervous system (CNS) involvement. Rituximab was effective in patients with or without prior immunosuppression. Histologic transformation to diffuse large B-cell lymphoma (DLBCL) or emergence of T-cell lymphomas occurred in immunochemotherapy non-responders or at relapse, emphasizing the role of re-biopsy in this subset of patients. At a median follow-up of 6 years, median event-free (EFS) and overall survival (OS) were 8.5 and 8.7 years, respectively. EFS was not significantly influenced by increasing IPI scores ( p  = 0.09), CNS involvement ( p  = 0.5), or immunosuppression at diagnosis ( p  = 0.2). There was a trend towards improved OS in patients who were on immunosuppressive therapy at diagnosis, however, this was not statistically significant, p  = 0.054. This is the first study to characterize EBV+ poly B-LPD within the ICC 2022 framework. Larger studies are needed to validate these findings, define prognostic markers and guide therapy.

Recent genetic and molecular classification of DLBCL has advanced our knowledge of disease biology, yet were not designed to predict early events and guide anticipatory selection of novel therapies. To address this unmet need, we used an integrative multiomic approach to identify a signature at diagnosis that will identify DLBCL at high risk of early clinical failure. Tumor biopsies from 444 newly diagnosed DLBCL were analyzed by WES and RNAseq. A combination of weighted gene correlation network analysis and differential gene expression analysis was used to identify a signature associated with high risk of early clinical failure independent of IPI and COO. Further analysis revealed the signature was associated with metabolic reprogramming and identified cases with a depleted immune microenvironment. Finally, WES data was integrated into the signature and we found that inclusion of ARID1A mutations resulted in identification of 45% of cases with an early clinical failure which was validated in external DLBCL cohorts. This novel and integrative approach is the first to identify a signature at diagnosis, in a real-world cohort of DLBCL, that identifies patients at high risk for early clinical failure and may have significant implications for design of therapeutic options.

Follicular lymphoma (FL) 3B is considered an aggressive lymphoma, however recent studies have challenged this paradigm. Additional controversy involves the clinical implication of pure FL3B (FL3Bp) vs FL3B with concurrent diffuse large B cell lymphoma (DLBCL) (FL3Bc). To address these questions, we performed a pooled study of the MER and LEO cohorts comparing 464 newly diagnosed, R-CHOP-treated patients with FL1-2 ( n  = 216), FL3A ( n  = 170), FL3B ( n  = 78) and 739 DLBCL. Among FL3B patients, 19 (24%) had FL3Bc and 59 (76%) FL3Bp. Baseline characteristics and outcomes were similar between the two FL3B subtypes. Compared to FL1-3A, FL3B showed similar clinical features, except for a lower tumor burden. After R-CHOP, FL1-2 patients had an inferior event-free survival (EFS) than those with FL3B, whereas there was no difference with FL3A. Survival was similar across the FL grades. Although FL1-2 patients failed to achieve EFS24 more frequently than FL3B and FL3A, FL3B patients who failed EFS24 had three-fold higher risk of subsequent mortality than other FLs. At 5-year follow-up FL3B patients had twice the risk of relapse with an aggressive subtype than those with FL1-2 and FL3A. Compared to DLBCL, FL3B patients had more favorable clinical features, but similar outcomes to GCB subtype. Our data suggest that most FL3B have a good outcome, while a subset has an aggressive behavior.

Up to 40% of diffuse large B-cell lymphoma (DLBCL) patients do not experience a durable response to frontline immunochemotherapy, and prospective identification of high-risk cases that may benefit from personalized therapeutic management remains an unmet need. Molecular phenotyping techniques have established a landscape of genomic variants in diagnostic DLBCL; however, these have not yet been applied in large-scale studies of relapsed/refractory DLBCL, resulting in incomplete characterization of mechanisms driving tumor progression and treatment resistance. Here, we performed an integrated multiomic analysis on 228 relapsed/refractory DLBCL samples, including 24 with serial biopsies. Refined cell-of-origin subtyping identified patients harboring GCB and DZsig+ relapsed/refractory tumors in cases with primary refractory disease with remarkably poor outcomes, and comparative analysis of genomic features between relapsed and diagnostic samples identified subtype-specific mechanisms of therapeutic resistance driven by frequent alteration to MYC , BCL2 , BCL6 , and TP53 among additional strong lymphoma driver genes. Tumor evolution dynamics suggest innate mechanisms of chemoresistance are present in many DLBCL tumors at diagnosis, and that relapsed/refractory tumors are primarily comprised of a homogenous clonal expansion with reduced tumor microenvironment activity. Adaptation of personalized therapeutic strategies targeting DLBCL subtype-specific resistance mechanisms should be considered to benefit these high-risk populations.