Previous work described 3 cases of CD4+ T-cell lymphomas harboring Merkel cell polyomavirus (MCPyV), as demonstrated by in situ hybridization (ISH), next generation sequencing, and polymerase chain reaction. Two of these cases were cutaneous T-cell lymphomas compatible with mycosis fungoides in postcardiac transplant patients, while the third was a peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), in a patient without known immunosuppression. In this study, we assess an expanded cohort of T-cell neoplasms from 4 institutions for expression of MCPyV by ISH. This cohort includes 9 T-cell lymphomas occurring in the post solid organ transplant setting, of which 5 (60%) were positive for MCPyV by ISH. Four of these cases were classified as PTCL-NOS and the remaining case as nodal T follicular helper cell lymphoma, angioimmunoblastic type. In addition, we performed MCPyV ISH on a variety of neoplastic and non-neoplastic lymphoid tissues from both transplant and nontransplant patients. No evidence of MCPyV infection was found in lymphoid tissues in the absence of T-cell lymphoma, suggesting that the presence of MCPyV is specific to this rare subset of T cell lymphomas. Furthermore, all MCPyV-positive T-cell lymphomas (8 of 8) were CD4+ and the large majority were observed in the post-transplant setting (7 of 8). Multiplex single-molecule fluorescence ISH confirmed the presence of MCPyV in CD4+ T-cells. These findings support the hypothesis that MCPyV infection is specifically associated with rare CD4+ T-cell lymphomas, particularly in transplant recipients.

Mantle cell lymphoma (MCL) is a rare, aggressive subtype of B-cell non-Hodgkin lymphoma with rare cutaneous involvement that typically indicates advanced systemic disease. We report a case of indolent MCL in a 56-year-old previously healthy male who presented with a 5-year history of edematous, painful plaques and associated onychodystrophy in the bilateral toes. Histopathology demonstrated a multinodular dermal and subcutaneous infiltrate of atypical lymphocytes. Immunohistochemistry revealed a primary B-cell population diffusely positive for CD20 and BCL2 and focally positive for BCL1. These cells were negative for CD5, SOX-11, BCL6, and LEF1. In situ hybridization demonstrated admixed lambda-restricted plasma cells, indicating plasmacytic differentiation. Fluorescence in situ hybridization testing for an IGH/CCND1 translocation was positive, confirming a diagnosis of MCL. While bone marrow biopsy demonstrated 10%-20% involvement by MCL, staging revealed no lymphadenopathy or visceral disease. No significant peripheral blood laboratory abnormality was noted. To our knowledge, this is the first reported case of cutaneous involvement by MCL confined to the bilateral toes. This case is also notable for its absence of typical markers, namely CD5 and SOX-11, plasmacytic differentiation, and indolent clinical behavior. We discuss the diagnostic and clinical significance of these atypical clinicopathologic features and diagnostic overlap with other cutaneous B-cell lymphomas, emphasizing the importance of comprehensive immunophenotypic and molecular evaluation in atypical presentations.

Myelodysplastic syndromes are clonal bone marrow failure disorders demonstrating variable degrees of cytopenias, morphologic dysplasia, and risk of progression to acute myeloid leukemia. We hypothesized that MDS with a normal karyotype (NK) would exhibit a unique mutational or morphologic signature. We investigated the morphologic features and genetic profiles of 89 patients with myelodysplastic syndrome (MDS), including 42 with a NK and 47 with an abnormal karyotype (non-NK). We used next-generation sequencing (NGS) to detect pathogenic variants and performed morphologic review by two independent hematopathologists in a blinded manner with a nested set of 43 control cases. NK and non-NK cases showed similar levels of dysplasia in granulocytes and erythroids, but non-NK cases showed significantly more dysplasia in megakaryocytes (P = 0.037). The mutational burden was similar between NK and non-NK cases. TET2 and SF3B1 mutations were more frequent in NK cases (P = 0.029 and P = 0.013, respectively), and TP53 mutations were more frequent in non-NK cases (P = 0.007). Overall, higher mutational burden was associated with higher levels of megakaryocyte dysplasia (P = 0.003), but there was no association with granulocytic or erythroid dysplasia. Cases with STAG2 mutations were associated with higher overall megakaryocyte dysplasia (P = 0.0016) and proportion of megakaryocytes with separate nuclear lobes (P < 0.0001). The megakaryocyte lineage is the most expressive in terms of reflecting morphologic dysplasia due to cytogenetic or molecular abnormalities. MDS with NK shows similar morphologic features to non-NK cases, but our findings suggest that non-NK cases exhibit higher levels of megakaryocytic dysplasia.

Implementing a new laboratory information system (LIS) presents an opportunity to improve operational efficiency and streamline reporting by refining workflows by utilizing LIS functionality. Flow cytometry laboratories face unique challenges because the specimen and test results may be categorized under clinical pathology (CP), anatomic pathology (AP), or both. We describe the design and implementation of reporting flow cytometry results within the Epic Beaker CP module, its interface with the Epic Beaker AP module, and integrated reporting for AP/CP cases at an academic institution. This manuscript emphasizes the challenges and steps needed to integrate anatomic and clinical pathology workflows by leveraging LIS functionality to implement electronic and predominantly paperless workflows within a flow cytometry laboratory.

We analyzed 268 patients with myelodysplastic syndromes (MDS) and chronic myelomonocytic leukemia (CMML) to determine the impact of their molecular taxonomic features on patient's clinical outcomes and responsiveness to therapy with hypomethylating agents (HMA). They were hierarchically classified via next-generation sequencing into molecular taxonomic groups based on previously described hierarchical mutational clusters (Bernard E et al, Blood 2024). The groups varied in size, molecular complexity and patient outcomes. With a median of 4 cycles of HMA-based regimens, 54 % patients were treated, with an overall response rate (ORR) of 35 % (IWG 2023 criteria). Focused evaluation of specific taxonomic subgroups demonstrated ORR in U2AF1 50 %, bi-TET2 44 %, SF3B1 40 %, TP53-multihit or CK 39 %, IDH-STAG2 36 %, SETBP1/-7 33 %, No molecular event 33 %, mNOS 28 %, CCUS-like 7 %. Notably, HMA response was not associated with International Prognostic Scoring System (IPSS-M) risk categories. The median follow-up time for the entire cohort was 4 years, with overall survival of 66 % and leukemia-free survival of 81 % at 3 years following initial diagnosis. Within the specific taxa these prognostic risk features were relatively higher for several taxonomic subgroups which were related to the patient's IPSS-M categorization. In contrast, our data demonstrated distinct differences of HMA responses within taxonomic subgroups, but without significant association between patients' HMA responses and their IPSS-M categorization. These findings indicate that molecular taxonomic classification could help refine therapeutic strategies for MDS and CMML, particularly in identifying subgroups more likely to benefit from HMA therapy.

OBJECTIVES:Measurable residual disease flow cytometry (MRD-FC) and molecular studies are the most sensitive methods for detecting residual malignant populations after therapy for TP53-mutated acute myeloid leukemia and myelodysplastic neoplasms (TP53+ AML/MDS). However, their sensitivity is limited in suboptimal aspirates or when the immunophenotype of the neoplastic blasts overlaps with erythroids or normal maturing myeloid cells. In this study, we set out to determine if p53 immunohistochemistry (IHC) correlates with MRD-FC and next-generation sequencing (NGS) in the posttherapy setting and to determine the utility of p53 IHC to detect residual disease in the setting of negative or equivocal MRD-FC. METHODS:We retrospectively identified 28 pre- and posttherapy bone marrow biopsy specimens from 9 patients with TP53+ AML/MDS and a p53 overexpressor phenotype by IHC (strong 3+ staining at initial diagnosis). Next-generation sequencing and/or MRD-FC results were collected for each specimen. RESULTS:Using a threshold of more than ten 2-3+ cells in any one 400× field, p53 IHC detected residual disease with a sensitivity of 94% and a specificity of 89%. The threshold used in this study showed a high degree of concordance among 6 blinded pathologists (Fleiss κ = 0.97). CONCLUSIONS:Our study suggests that p53 IHC can be used as a rapid tool (within 24 hours) to aid in the detection of residual disease that may complement MRD-FC or NGS in cases in which the flow cytometry immunophenotype is equivocal and/or the bone marrow aspirate is suboptimal.

The related myeloid malignancies myelodysplastic syndromes (MDS) and chronic myelomonocytic leukemia (CMML) may be classified into hierarchically characterized molecular taxonomic subgroups delineated by their oncogenic mutations and other molecular features (Bernard E et al, Blood 2024, PMID:38958467, ASH 2023, 997a, reference 1). In this single-center study, we evaluated an independent group of 267 patients (212 MDS and 55 CMML) at our institution between 2018 through 2023 to determine the impact of their molecular taxonomic features on patient's clinical outcomes and responsiveness to therapy with hypomethylating agents (HMA). Classification of patients was performed by WHO 2022 and ICC, all of whom had NGS testing: 88% performed at Stanford utilizing an internal NGS panel targeting 164 recurrently mutated genes in myeloid and lymphoid malignancies with a minimum variant allele fraction (VAF) of 2%, the remaining 12% had NGS testing done externally with similar gene coverage. The median age at diagnosis was 72 years (yr) (IQR 66-79 yr); 238 (89%) patients were primary and 29 (11%) were therapy-related; 66% were male. 20% patients transformed to AML. Median follow-up was 3.2 yr. Patients were delineated into 18 hierarchical molecular taxonomic groups and subdivided into four previously described hierarchical clusters (per reference 1): Group1: Well-established (26%: DDX41, AML-like, TP53-complex, t(1;17), SETBP1/-7, del(5q)); Group 2: Previously reported (27%: EZH2-ASXL1, IDH-STAG2, BCOR/L1, bi-TET2); Group 3: Splice gene (22%: U2AF1, SRSF2, ZRSR2, SF3B1); and Group 4: Residual [25%: CCUS-like (DNMT3A, TET2), mNOS (other recurrent mutations), & No-event molecular groups]. Although nearly all groups were present in both MDS and CMML, increased Group 1 (31 v 2%) and taxa SF3B1 (15 v 0%) were noted in MDS and increased bi-TET2 (47 v 4%) in CMML patients, p=0.001, 0.002, 0.001, respectively,related to their known genetic propensities. With a median of 4 (IQR 3-6) cycles of HMA-based regimens, 54% (N=144) patients were treated. Most patients (78%) received decitabine or azacitidine monotherapy, the remainder in combination with other agents. The overall response rate (ORR), based on the International Working Group 2023 criteria (CR or CR equivalent + Hematologic Improvement), was 34%, with similar findings for MDS and CMML patients: 35% & 34%, respectively. Focused evaluation of specific taxonomic subgroups demonstrated ORR in:TP53-complex 39%, SETBP1/-7 33%, IDH-STAG2 36%, bi-TET2 41%, U2AF1 50%, SF3B1 40%, CCUS-like 7%, mNOS 33%, No event 33%. The HMA responses were not associated with the patients' IPSS-M prognostic risk categories/scores, ie, the ORR varied unrelatedly for each taxa (p=0.61, Logistic regression).The medianoverall survival (OS) of the entire cohort was 3.2 yr with OS 56% & AML transformation 20% at 3 yr. For the specific taxa these features were: TP53-complex 1.1 yr & 33%, IDH-STAG2 2.4 yr & 42%, BCOR 2.8 yr & 38%, SRSF2 2.8 yr & 33%, SETBP1/-7 2.9 yr & 8%, bi-TET2 3.9 yr & 20%, U2AF1 3.9 yr & 11%, SF3B1 3.7 yr & 0, CCUS-like 2.8 yr & 20%, mNOS 4.1 yr & 17%, No event 3.4 yr & 13%. In contrast to ORR, these two clinical outcome features for the specific taxa were both related to the patient's IPSS-M categorization (p ≤0.001 & ≤0.001, Cox regression, respectively). These data indicate that despite OS and PFS of MDS/CMML patients being related to both their molecular taxonomic subgroups and IPSS-M classification, there is not a significant association between patients' HMA responses and their IPSS-M classification, albeit findings being limited by small taxa sample sizes. These features provide data supporting the potential for focusing on specific molecular subgroups of MDS and CMML patients for more precise therapeutic targeting of HMAs.

BACKGROUND:Epstein-Barr virus (EBV)-associated post-transplant lymphoproliferative disorders (PTLD) is the most common malignancy in children after transplant; however, difficulties for early detection may worsen the prognosis. METHODS:The prospective, multicenter, study enrolled 944 children (≤21 years of age). Of these, 872 received liver, heart, kidney, intestinal, or multivisceral transplants in seven US centers between 2014 and 2019 (NCT02182986). In total, 34 pediatric EBV+ PTLD (3.9%) were identified by biopsy. Variables included sex, age, race, ethnicity, transplanted organ, EBV viral load, pre-transplant EBV serology, immunosuppression, response to chemotherapy and rituximab, and histopathological diagnosis. RESULTS:The uni-/multivariable competing risk analyses revealed the combination of EBV-seropositive donor and EBV-naïve recipient (D+R-) was a significant risk factor for PTLD development (sub-hazard ratio: 2.79 [1.34-5.78], p = .006) and EBV DNAemia (2.65 [1.72-4.09], p < .001). Patients with D+R- were significantly more associated with monomorphic/polymorphic PTLD than those with the other combinations (p = .02). Patients with monomorphic/polymorphic PTLD (n = 21) had significantly more EBV DNAemia than non-PTLD patients (p < .001) and an earlier clinical presentation of PTLD than patients with hyperplasias (p < .001), within 6-month post-transplant. Among non-liver transplant recipients, monomorphic/polymorphic PTLD were significantly more frequent than hyperplasias in patients ≥5 years of age at transplant (p = .01). CONCLUSIONS:D+R- is a risk factor for PTLD and EBV DNAemia and associated with the incidence of monomorphic/polymorphic PTLD. Intensive follow-up of EBV viral load within 6-month post-transplant, especially for patients with D+R- and/or non-liver transplant recipients ≥5 years of age at transplant, may help detect monomorphic/polymorphic PTLD early in pediatric transplant.

A teenage girl presented with fevers of unknown origin and pancytopenia. Complete blood count showed anemia (hemoglobin, 9.0 g/dL), neutropenia (1.7 × 10 9 /L), and thrombocytopenia (66 × 10 9 /L). The bone marrow was hypocellular with left shifted hematopoiesis and myeloid hypoplasia. Aspirate smears were notable for a prominent population of neutrophils with crescentic nuclei that engulfed blue amorphous material (Fig. 1 panels A and B, Wright-Giemsa, magnification × 1000). The trephine biopsy showed similar cells with crescentic nuclei and eosinophilic material (Fig. 1 panels C and D, hematoxylin and eosin × 400). Flow cytometry was negative for an abnormal population. EBV by in situ hybridization and parvovirus immunohistochemistry were negative. Subsequent serologic testing was positive for ANA (1:1280), low C3/C4, anti-dsDNA, anti-SM and anti-B2GP1. A kidney biopsy demonstrated findings consistent with class III lupus nephritis.

The accurate classification of lymphoma subtypes using hematoxylin and eosin (H&E)-stained tissue is complicated by the wide range of morphological features these cancers can exhibit. We present LymphoML - an interpretable machine learning method that identifies morphologic features that correlate with lymphoma subtypes. Our method applies steps to process H&E-stained tissue microarray cores, segment nuclei and cells, compute features encompassing morphology, texture, and architecture, and train gradient-boosted models to make diagnostic predictions. LymphoML's interpretable models, developed on a limited volume of H&E-stained tissue, achieve non-inferior diagnostic accuracy to pathologists using whole-slide images and outperform black box deep-learning on a dataset of 670 cases from Guatemala spanning 8 lymphoma subtypes. Using SHapley Additive exPlanation (SHAP) analysis, we assess the impact of each feature on model prediction and find that nuclear shape features are most discriminative for DLBCL (F1-score: 78.7%) and classical Hodgkin lymphoma (F1-score: 74.5%). Finally, we provide the first demonstration that a model combining features from H&E-stained tissue with features from a standardized panel of 6 immunostains results in a similar diagnostic accuracy (85.3%) to a 46-stain panel (86.1%).

CONTEXT.—:Stanford Pathology began stepwise subspecialty implementation of whole slide imaging (WSI) in 2018 soon after the first US Food and Drug Administration approval. In 2020, during the COVID-19 pandemic, the Centers for Medicare & Medicaid Services waived the requirement for pathologists to perform diagnostic tests in Clinical Laboratory Improvement Amendments (CLIA)-licensed facilities. This encouraged rapid implementation of WSI across all surgical pathology subspecialties. OBJECTIVE.—:To present our experience with validation and implementation of WSI at a large academic medical center encompassing a caseload of more than 50 000 cases per year. DESIGN.—:Validation was performed independently for 3 subspecialty services with a diagnostic concordance threshold above 95%. Analysis of user experience, staffing, infrastructure, and information technology was performed after department-wide expansion. RESULTS.—:Diagnostic concordance was achieved in 96% of neuropathology cases, 100% of gynecologic pathology cases, and 98% of immunohistochemistry cases. After full implementation, 8 high-capacity scanners were operational, with whole slide images generated on greater than 2000 slides per weekday, accounting for approximately 80% of histologic slides at Stanford Medicine. Multiple modifications in workflow and information technology were needed to improve performance. Within months of full implementation, most attending pathologists and trainees had adopted WSI for primary diagnosis. CONCLUSIONS.—:WSI across all surgical subspecialities is achievable at scale at an academic medical center; however, adoption required flexibility to adjust workflows and develop tailored solutions. WSI at scale supported the health and safety of medical staff while facilitating high-quality patient care and education during COVID-19 restrictions.

Epstein-Barr virus (EBV)–positive posttransplant lymphoproliferative disorder (PTLD) results in significant morbidity and mortality in pediatric transplant recipients. Identifying individuals at an increased risk of EBV-positive PTLD could influence clinical management of immunosuppression and other therapies, improving posttransplant outcomes. A 7-center prospective, observational clinical trial of 872 pediatric transplant recipients evaluated the presence of mutations at positions 212 and 366 of EBV latent membrane protein 1 (LMP1) as an indicator of risk of EBV-positive PTLD (clinical trials: NCT02182986). DNA was isolated from peripheral blood of EBV-positive PTLD case patients and matched controls (1:2 nested case:control), and the cytoplasmic tail of LMP1 was sequenced. Thirty-four participants reached the primary endpoint of biopsy-proven EBV-positive PTLD. DNA was sequenced from 32 PTLD case patients and 62 matched controls. Both LMP1 mutations were present in 31 of 32 PTLD cases (96.9%) and in 45 of 62 matched controls (72.6%) (P = .005; OR = 11.7; 95% confidence interval, 1.5, 92.6). The presence of both G212S and S366T carries a nearly 12-fold increased risk of development of EBV-positive PTLD. Conversely, transplant recipients without both LMP1 mutations carry a very low risk of PTLD. Analysis of mutations at positions 212 and 366 of LMP1 can be informative in stratifying patients for risk of EBV-positive PTLD.

Tajima, Tetsuya1; Bernstein, Daniel2; Boyd, Scott D3; Gratzinger, Dita3; Lum, Grant1; Sasaki, Kazunari1; Tan, Brent3; Weinberg, Kenneth2; Armstrong, Brian4; Brown, Meredith5; Chin, Clifford6; Desai, Dev7; Fishbein, Thomas M8; Mazariegos, George9; Robien, Mark A5; Tekin, Akin10; Twist, Clare J11; Venick, Robert S12; Krams, Sheri M1; Martinez, Olivia M1; Esquivel, Carlos O1 Author Information

Introduction: Myelodysplastic syndromes (MDS) are a spectrum of clonal bone marrow failure disorders demonstrating cytopenias, dysplasia, and risk of progression. Although ~50% of MDS patients have normal karyotype (NK), a subset of MDS exhibits genetic alterations that result in an abnormal karyotype. However, the relationship between the molecular landscape and histologic features in MDS have not been well explored. Using next generation sequencing (NGS) and cytogenetics, we sought to correlate genetic abnormalities in MDS with morphologic dysplasia. Methods: After IRB approval, we retrospectively identified NGS studies performed with a 164 gene panel in patients with MDS at Stanford (2018-2021). Molecular and cytogenetic data were collected for 225 MDS patients. Peripheral blood and bone marrow (BM) slides were collected from 61 patients for histological review. As controls, 32 staging BMs were obtained from untreated lymphoma patients. A hematopathologist performed a blinded intense morphologic review. A subset of cases was reviewed by 2 other hematopathologists and the intraclass correlation coefficient (ICC) was calculated to evaluate concordance. The degree of dysplastic features and overall dysplasia was scored. The standardized mean difference (SMD) was calculated to quantify the degree of dysplasia between comparison groups. Statistical analysis was performed using R (3.6.3); p value < 0.05 was considered statistically significant. Results: MDS cases had higher degrees of dysplasia than control cases in megakaryocytic (median 37.5% vs 0%), granulocytic (median 20% vs 0%), and erythroid (median 10% vs 0%) lineages. To assess specificity, using a cutoff of 10%, 1/31 control cases (3.1%) showed megakaryocytic dysplasia, 2/32 (6.3%) had erythroid dysplasia, while none showed granulocytic dysplasia. Dysplasia in > 2 lineages in >10% of cells was specific for MDS, detected in 49/61 (80.3%) of MDS cases vs 0/32 control cases (Table 1). Within the MDS group, lack of multilineage dysplasia was more common in NK (8/25; 32%) vs non-NK (3/36; 8.3%), suggesting MDS-NK is morphologically subtle. Using a cutoff of 10%, 13/25 (52%) NK lacked granulocytic dysplasia vs 10/36 (27.8%) in non-NK, 8/25 (32%) of NK lacked erythroid dysplasia vs 10/36 (27.8%) in non-NK, and 5/25 (20%) NK lacked megakaryocytic dysplasia vs 3/35 (8.3%) in non-NK. The most strongly associated dysplastic features for MDS included erythroid megaloblastic change (SMD=1.25), erythroid nuclear features (SMD=1.041), atypical megakaryocyte nuclei (SMD=1.189), separated megakaryocyte nuclei (SMD=1.131), and hypogranulated granulocytes (SMD=1.096). Based on 10 MDS and 5 control cases, rough concordance on overall dysplasia was demonstrated among 3 hematopathologists. Granulocytic dysplasia showed the highest reproducibility (ICC for granulocytic = 0.948, erythroid = 0.547, megakaryocytic = 0.531). The percent of cells with dysplasia in the MDS cohort did not correlate with number of mutations. The overall number of mutations between MDS with NK and non-NK were relatively similar (Figure 1). The non-NK group exhibited a greater frequency of pathogenic TP53 variants than NK (31.5% vs 2.6%, p < 0.0001). Conversely, SF3B1 and TET2variants occurred more frequently in the NK cohort than non-NK (SF3B1: 32.5% vs 12.6%; TET2: 29.8% vs 12.6%, both p values < 0.003). In MDS cases with a TET2 variant, NK was associated with a significantly higher total number of mutations than non-NK cases (median [IQR]: 5[5-7] vs 4[3-6], p = 0.031). Using Random Forest models, exploratory multivariate analysis identified the presence of mutations in TP53, SF3B1, TET2, and overall megakaryocytic, granulocytic, and erythroid dysplasia as the prominent parameters that distinguished NK from non-NK MDS cases. There was no significant difference in age at diagnosis between NK and non-NK MDS in all NGS cases (median age 74 vs 70, p = 0.10) and morphologically scored cases (median age 70 in both groups). Conclusion: Our study demonstrates that granulocytic dysplasia was the most specific morphologic finding for MDS with high reproducibility among 3 hematopathologists. Detection of dysplasia in > 2 lineages in >10% cells was also specific for MDS, while MDS-NK appear morphologically subtle. Mutations in TET2 were more frequent in MDS-NK. Our findings highlight the importance of NGS and histopathology in helping establish a diagnosis of MDS-NK. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

OBJECTIVESHistiocytic neoplasms demonstrate shared gene translocations and clonal immunoglobulin gene rearrangements in cases of associated B-cell lymphomas. However, the evolution of these related disease processes remains largely uncertain, especially in the setting of a prior mantle cell lymphoma.METHODSWe describe a unique case of a histiocytic sarcoma that transdifferentiated from blastoid mantle cell lymphoma after extensive therapy. Cytogenic and molecular studies were performed and provided evidence for clonal progression.RESULTSWe present the first reported case of a patient with blastoid mantle cell lymphoma harboring a CCND1 rearrangement that progressed despite multiple therapeutic regimens and ultimately transdifferentiated into histiocytic sarcoma. The histiocytic sarcoma demonstrated a CCND1 rearrangement and targeted next-generation sequencing showed a pathogenic variant in NRAS, a gene involved in the RAS/MAPK pathway, known to play a role in the pathogenesis of histiocytic sarcomas. TP53, NOTCH2, CREBBP, and NFKBIE variants were also identified, which are often seen in B-cell lymphomas, while rarely described in histiocytic sarcoma.CONCLUSIONSTo our knowledge, this is the first report to provide evidence for clonal evolution of histiocytic sarcoma from blastoid mantle cell lymphoma based on cytogenic and molecular findings. The patient's protracted therapeutic course may have acted as an evolutionary driver promoting this transdifferentiation process.

The diagnosis of angioimmunoblastic T-cell lymphoma (AITL) is complex and requires the demonstration of a T-follicular helper (TFH) phenotype. Immunophenotypic markers that detect the TFH phenotype are highly variable, thereby necessitating the use of 3 to 5 TFH markers to substantiate a TFH phenotype. We tested the utility of germinal center markers human germinal center–associated lymphoma (HGAL) and LIM-domain only 2 (LMO2) in detecting a TFH phenotype. We compared their staining to that of 6 TFH markers in current use, PD-1, ICOS, CXCL13, SAP, CD10, and BCL6, in a cohort of 23 AITL. Our results show that although both markers can detect a TFH phenotype, HGAL was superior to LMO2 in the percent of cells stained and the intensity of staining, 2 variables used to generate H -scores. Using H -scores as the metric, HGAL was most comparable to BCL6 among the currently used TFH markers and was more sensitive than CXCL13, SAP, CD10, and LMO2. PD-1 and ICOS emerged as the most robust of the 8 markers tested in this study in detecting a TFH phenotype. We conclude that HGAL is a reliable marker of TFH cells and can aid in the diagnosis of lymphomas of TFH derivation, particularly in the recognition of early patterns of AITL.