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The International Pediatric Transplant Association (IPTA) convened an expert consensus conference to assess current evidence and develop recommendations for various aspects of care relating to post-transplant lymphoproliferative disorder after solid organ transplantation in children. In this report from the Prevention Working Group, we reviewed the existing literature regarding immunoprophylaxis and chemoprophylaxis, and pre-emptive strategies. While the group made a strong recommendation for pre-emptive reduction of immunosuppression at the time of EBV DNAemia (low to moderate evidence), no recommendations for use could be made for any prophylactic strategy or alternate pre-emptive strategy, largely due to insufficient or conflicting evidence. Current gaps and future research priorities are highlighted.

Background Histiocytic and dendritic cell neoplasms are a diverse group of tumors arising from monocytic or dendritic cell lineage. Whereas the genomic features for Langerhans cell histiocytosis and Erdheim‐Chester disease have been well described, other less common and often aggressive tumors in this broad category remain poorly characterized, and comparison studies across the World Health Organization diagnostic categories are lacking. Methods Tumor samples from a total of 102 patient cases within four major subtypes of malignant histiocytic and dendritic cell neoplasms, including 44 follicular dendritic cell sarcomas (FDCSs), 41 histiocytic sarcomas (HSs), 7 interdigitating dendritic cell sarcomas (IDCSs), and 10 Langerhans cell sarcomas (LCSs), underwent hybridization capture with analysis of up to 406 cancer‐related genes. Results Among the entire cohort of 102 patients, CDKN2A mutations were most frequent across subtypes and made up 32% of cases, followed by TP53 mutations (22%). Mitogen‐activated protein kinase (MAPK) pathway mutations were present and enriched among the malignant histiocytosis (M) group (HS, IDCS, and LCS) but absent in FDCS (72% vs. 0%; p, Histiocytic and dendritic cell neoplasms are a diverse group of tumors arising from the monocytic or dendritic cell lineage. This article presents the molecular characteristics of the four major subtypes of malignant histiocytic and dendritic cell neoplasms, focusing on genomic alterations that could represent therapeutic targets.

Objectives Coronavirus disease 19 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is associated with diverse clinical, including hematologic, abnormalities. We describe peripheral blood and bone marrow findings in deceased and living patients with COVID-19. Methods We examined bone marrows from 20 autopsies and 2 living patients with COVID-19 using H&E-stained slides and immunohistochemical stains. Clinical history and laboratory values were reviewed. HScore was calculated to estimate risk of hemophagocytic lymphohistocytosis (HLH). Results The deceased patients included 12 men and 8 women (aged 32 to >89 years; median, 63 years). Hematologic abnormalities included frequent neutrophilic leukocytosis, lymphopenia, anemia, and thrombocytopenia; one patient showed striking erythrocytosis. The bone marrows were all normocellular to hypercellular, most showing maturing trilineage hematopoiesis with myeloid left shift. In all 19 evaluable bone marrows, hemophagocytic histiocytes were identified. The HScore for secondary HLH ranged from 35 to 269 (median, 125; >169 in 5 patients). Coinfections were identified in 6 patients. In 2 living patients, bone marrow showed maturing trilineage hematopoiesis, including one showing few hemophagocytic histiocytes. Conclusions Peripheral blood from deceased patients with COVID-19 frequently showed neutrophilic leukocytosis, lymphopenia, and, rarely, secondary polycythemia; hemophagocytosis was common in their bone marrow. Consistent with other studies, we provide histopathologic evidence of secondary HLH development in patients with COVID-19.

Detailed information regarding follow-up of ocular adnexal lymphoma and of the frequency of large cell transformation of low-grade ocular adnexal lymphoma is limited. We studied 174 patients with ocular adnexal lymphoma (OAL) to evaluate long-term clinical outcome and patterns of failure. All lymphomas presenting with involvement of the ocular adnexa diagnosed at the Massachusetts General Hospital (MGH) between 1974 and 2007, in which at least 6 months of follow-up was available, were included in this study. There were 106 extranodal marginal zone lymphomas (MALT lymphomas, MZL), 40 follicular lymphomas (FL), 16 diffuse large B cell lymphomas (DLBCL), 5 mantle cell lymphomas (MCL), 3 small lymphocytic lymphomas/chronic lymphocytic leukemias, 1 lymphoplasmacytic lymphoma, 2 B lymphoblastic lymphomas, and 1 extranodal NK/T cell lymphoma. Relapses occurred in 42 of 106 MZL patients (40%) and in 14 of 40 FL patients (35%). Two MZL and one FL progressed to DLBCL. Five and 10-year relapse-free survival (RFS) and five and 10-year overall survival (OS) respectively were: MZL 67%, 36%, 93%, 88%; FL: 54%, 32%, 90%, 82%; DLBCL: 79%, 79% 88%, 88% MCL: 20%, 0%, 100%, 25%. MZL and FL patients often developed relapses but had long survival; progression to DLBCL was uncommon. DLBCL had a favorable prognosis. MCL had a poor prognosis.

ObjectivesTo define the clinicopathologic features of extranodal marginal zone lymphoma (EMZL) of the central nervous system (CNS), including cases arising in CNS parenchyma, which have been reported only rarely.MethodsTwelve cases of CNS EMZL were identified, including 5 based in CNS parenchyma and 7 nonparenchymal cases arising in dura or choroid plexus.ResultsHistologically, parenchymal cases were perivascular infiltrates without a dominant lymphoid mass, whereas nonparenchymal cases were masses of small lymphocytes. Plasma cells were a larger component of the infiltrate in parenchymal cases (median, 30%; range, 20%-50%) than nonparenchymal cases (median, 0%; range, 0%-5%; P < .001), and plasma cells were clonal by immunohistochemistry in 4 of 5 parenchymal vs 1 of 7 nonparenchymal cases (P = .07). Fluorescence in situ hybridization for MALT1 rearrangement was positive in 1 of 3 parenchymal and none of 3 nonparenchymal cases. Chromosomal microarray was abnormal in 5 of 7 cases (71%), with chromosome 6/6q alterations identified in 3 cases. No patients with parenchymal disease but all 6 (100%) with nonparenchymal disease achieved complete remission.ConclusionsThis case series, the first to include multiple parenchymal cases, clarifies the spectrum of clinical, pathologic, and genetic findings in CNS EMZL and suggests that parenchymal-based lesions may show less favorable prognosis than dural-based disease.

Session 2 of the 2018 European Association of Hematopathology/Society for Hematopathology Workshop focused on lymphomas arising in immune-privileged sites: both lymphomas arising in the traditionally described "immune sanctuary" sites of the central nervous system (CNS) and testes, as well as those arising at sites of local immune privilege. Primary CNS large B cell lymphoma and primary testicular large B cell lymphoma were discussed, and the biology of these unique tumors was highlighted by several cases showing the classic mutation profile including MYD88 L265P and CD79B. The tendency of these tumors to involve both the CNS and testis was also reinforced by several cases. Four cases of low-grade B cell lymphomas (LGBCL) of the CNS were discussed. Two were classic Bing-Neel syndrome associated with LPL, and two were LGBCL with plasmacytic differentiation and amyloid deposition without systemic disease. Rare examples of systemic T and NK cell lymphomas involving the CNS were also discussed. Several cases of breast implant-associated anaplastic large cell lymphoma (BI-ALCL) were submitted showing the typical clinicopathologic features. These cases were discussed along with a case with analogous features arising in a patient with a gastric band implant, as well as large B cell lymphomas arising alongside foreign materials. Finally, large B cell lymphomas arising in effusions or localized sites of chronic inflammation (fibrin-associated diffuse large B cell lymphoma [DLBCL] and DLBCL associated with chronic inflammation) were described. The pathogenesis of all of these lymphomas is believed to be related to decreased immune surveillance, either innate to the physiology of the organ or acquired at a local site.

Objectives Primary central nervous system anaplastic large cell lymphoma, anaplastic lymphoma kinase positive (primary CNS ALCL, ALK+) is a rare CNS lymphoma whose description is limited to case reports. These tumors have a variable clinical course, and prognosis is primarily determined by age. We present the largest case series to date of primary CNS ALCL, ALK+, with observational data. Methods A retrospective search of multiple academic centers was performed to identify cases of primary CNS ALCL, ALK+. We also performed a review of published cases of primary CNS ALCL, ALK+. Clinical history, radiography, pathology, and genetic testing data were obtained to determine the prognostic implications in the context of clinical course. Results We identified three cases of primary CNS ALCL, ALK+ from our databases. A literature review identified 30 published reports of 31 individual cases. Clinical features for the combined 34 cases included a median age of 18.5 years, with a male to female ratio of 4.7:1, and the most common symptom was headache. Genetic studies demonstrated an ALK rearrangement by fluorescence in situ hybridization, and a gene fusion assay confirmed an NPM1-ALK gene fusion in one case. Conclusions We present the largest case series to date of a rare primary CNS lymphoma with additional diagnostic and clinical information.

This paper summarizes two sessions of the workshop during the XIX meeting of the European Association for Haematopathology (EAHP) held in Edinburgh in September 2018 dedicated to lymphomas of the gastrointestinal tract. The first session focused on the clinical and pathological features of primary gastrointestinal T cell and NK-cell lymphoproliferative disorders. The distinction between precursor lesions (RCD type 2) and enteropathy-associated T cell lymphoma were stressed, including the discussion of new diagnostic markers for the identification of aberrant phenotypes. Indolent T cell lymphoproliferative disorders of the gastrointestinal tract cases showed phenotypic heterogeneity with novel molecular alterations in few cases, such as STAT3-JAK2 fusion. In addition, novel clonal markers of disease, such as AXL and JAK3 somatic variants support the neoplastic nature of NK-cell enteropathy. The session on gastrointestinal tract B cell lymphoproliferations was dedicated to B cell lymphoproliferative disorders that arise primarily in the gastrointestinal tract (i.e., duodenal-type follicular lymphoma) or preferentially involve the digestive tract, such as large B cell lymphoma with IRF4 translocation and mantle cell lymphoma (MCL), including diverse molecular subtypes (i.e., CCND3-positive MCL mimicking MALT lymphoma). Challenging cases of high-grade B cell lymphomas with complex genetic profiles demonstrated the usefulness of novel molecular diagnostic methods such as targeted NGS to identify high-risk genetic features with potential clinical impact.

The genetic alterations that define primary central nervous system lymphoma (PCNSL) are incompletely elucidated, and the genomic evolution from diagnosis to relapse is poorly understood. We performed whole-exome sequencing (WES) on 36 PCNSL patients and targeted MYD88 sequencing on a validation cohort of 27 PCNSL patients. We also performed WES and phylogenetic analysis of 3 matched newly diagnosed and relapsed tumor specimens and 1 synchronous intracranial and extracranial relapse. Immunohistochemistry (IHC) for programmed death-1 ligand (PD-L1) was performed on 43 patient specimens. Combined WES and targeted sequencing identified MYD88 mutation in 67% (42 of 63) of patients, CDKN2A biallelic loss in 44% (16 of 36), and CD79b mutation in 61% (22 of 36). Copy-number analysis demonstrated frequent regions of copy loss (ie, CDKN2A), with few areas of amplification. CD79b mutations were associated with improved progression-free and overall survival. We did not identify amplification at the PD-1/PD-L1 loci. IHC for PD-L1 revealed membranous expression in 30% (13 of 43) of specimens. Phylogenetic analysis of paired primary and relapsed specimens identified MYD88 mutation and CDKN2A loss as early clonal events. PCNSL is characterized by frequent mutations within the B-cell receptor and NF-κB pathways. The lack of PD-L1 amplifications, along with membranous PD-L1 expression in 30% of our cohort, suggests that PD-1/PD-L1 inhibitors may be useful in a subset of PCNSL. WES of PCNSL provides insight into the genomic landscape and evolution of this rare lymphoma subtype and potentially informs more rational treatment decisions.

Lymphadenopathy is common in patients with immunoglobulin G4-related disease (IgG4-RD). However, the described histopathologic features of IgG4-related lymphadenopathy have been shown to be largely nonspecific. In an attempt to identify features specific for nodal IgG4-RD we examined the histopathologic features of lymph nodes from 41 patients with established IgG4-RD, with comparison to 60 lymph nodes from patients without known or subsequent development of IgG4-RD. An increase in immunoglobulin (Ig) G4-positive plasma cells >100/HPF and IgG4/IgG ratio >40% was identified in 51% of IgG4-RD cases and 20% of control cases. Localization of increased IgG4-positive plasma cells and IgG4/IgG ratio to extrafollicular zones was highly associated with IgG4-RD, particularly when identified in regions of nodal fibrosis (P

The diagnosis of lymphoma has evolved tremendously over time. Initially, diagnosis of lymphoma was largely based on morphology alone. Over time, immunophenotyping using flow cytometry and immunohistochemistry, and then in situ hybridization, have contributed dramatically to the pathologist's ability to recognize, diagnose and subclassify lymphomas more precisely. In recent years, cytogenetic and molecular genetic techniques have developed that allow evaluation of abnormalities in lymphomas, leading to an understanding of their pathogenesis and opening the door to targeted therapies that will lead to better outcomes for lymphoma patients.

Primary cutaneous marginal zone lymphoma (PCMZL) is the second most common B-cell lymphoma of the skin. A recent study has demonstrated a strikingly high prevalence of immunoglobulin (Ig)G4 expression in PCMZL with plasmacytic differentiation.The objective was to investigate the incidence of IgG4 expression in PCMZL, and its correlation with clinical and immunophenotypic features.Multicenter study that utilized immunohistochemistry and in-situ hybridization to evaluate the expression of IgG4, Ig light (κ and λ), and heavy chains (IgM, IgG), and the ratio of T (CD3+) and B (CD20+) cells in biopsy specimens from 30 patients with PCMZL and to correlate these findings with the clinical features.IgG4 expression was observed in 4 out of 30 patients (13%) with PCMZL. Patients with IgG4-positive lymphomas were 57 to 77 years of age (mean, 69) at biopsy. The lesions were solitary in 2 patients with IgG4-positive lymphomas, and were most commonly located on the trunk. Patients with IgG4-negative lymphomas experienced earlier disease onset at an average age of 53 years. The majority of the IgG4-negative cases presented with localized disease, on the trunk and upper extremities. There was no significant difference in the IgG4-positive versus negative cases for the following parameters: Ig κ or λ restriction, B-cell or T-cell predominance, and site of the lesions.IgG4 expression was observed in a minority of PCMZL patients. We did not identify significant clinical or immunophenotypic differences between IgG4 positive and negative cases.

Syphilis, a sexually transmitted infection caused by the Gram-negative bacterium Treponema pallidum, is increasing in prevalence in the United States. It has been our experience that primary and secondary syphilis of the aerodigestive tract can afflict a large age spectrum with varied clinical and histopathologic findings, which can lead to diagnostic problems and frequent misdiagnosis. In this study, we describe the histopathologic patterns of syphilis of the aerodigestive tract to expand awareness of its varied appearance. We identify 3 patterns of inflammatory response to syphilis: plasma cell-rich, lymphohistiocytic, and lymphoma-like. We also report the presence of immunoglobulin G4-predominant plasma cells in the inflammatory response as a potential mimicker of immunoglobulin G4-related disease. Lastly, we found that use of T. pallidum immunohistochemical stain is more reliable than Steiner silver stain at the identification of spirochetes. Our study highlights that despite convention, plasma cells are not always abundant in syphilis. Awareness of the histopathologic range of syphilis in the aerodigestive tract by the surgical pathologist can lead to the correct diagnosis and guide appropriate treatment.

Lymphomas that occur in the setting of IgG4-related disease (IgG4-RD) are uncommon. Most reported cases derive from Asia and are MALT lymphomas occurring in orbital IgG4-RD. The spectrum of lymphomas among IgG4-RD patients in the Western world remains poorly defined. The aim of this study was to report our experience with lymphomas occurring in IgG4-RD. Eight cases were identified from the pathology and consultation files. The median age was 61 years (range 22-68) at IgG4-RD diagnosis and 63.5 years (range 33-79) at lymphoma diagnosis, with a M:F ratio of 4:4. The diagnosis of lymphoma and IgG4-RD was concurrent in three cases and asynchronous in five (interval 4.3-16.4 years). Concurrent cases included a MALT lymphoma and a diffuse large B cell lymphoma (DLBCL) occurring with IgG4-related sialadenitis and a follicular lymphoma occurring with orbital IgG4-RD. Asynchronous cases included a lymphoplasmacytic lymphoma with large cell transformation and intervening IgG4-related pancreatitis, a MALT lymphoma after lacrimal IgG4-RD, two DLBCLs after multiorgan IgG4-RD, and a DLBCL after IgG4-related sialadenitis. Our findings suggest that lymphomas in IgG4-RD are more varied in location and type than the experience reported from Asia to date. Pathologists should be aware of the potential for lymphoma to develop in patients with IgG4-RD and should have a high degree of suspicion when lymphadenopathy or extranodal masses persist despite appropriate therapy for IgG4-RD. The co-occurrence of IgG4-RD and lymphoma that is reported here and previously suggests a possible etiologic association.

Gray zone lymphoma (GZL) is described as sharing features with classical Hodgkin lymphoma (cHL) and diffuse large B-cell lymphoma (DLBCL). However, there remains complexity in establishing diagnosis, delineating prognosis, and determining optimum therapy. Sixty-eight cases diagnosed as GZL across 15 North American academic centers were evaluated by central pathology review to achieve consensus. Of these, only 26 (38%) were confirmed as GZL. Morphology was critical to GZL consensus diagnosis (eg, tumor cell richness); immunohistochemistry showed universal B-cell derivation, frequent CD30 expression, and rare Epstein-Barr virus (EBV) positivity (CD20+, 83%; PAX5+, 100%; BCL6+, 20%; MUM1+, 100%; CD30+, 92%; EBV+, 4%). Forty-two cases were reclassified: nodular sclerosis (NS) cHL, n = 27 (including n = 10 NS grade 2); lymphocyte predominant HL, n = 4; DLBCL, n = 4; EBV+ DLBCL, n = 3; primary mediastinal large BCL n = 2; lymphocyte-rich cHL and BCL-not otherwise specified, n = 1 each. GZL consensus-confirmed vs reclassified cases, respectively, more often had mediastinal disease (69% vs 41%; P = .038) and less likely more than 1 extranodal site (0% vs 25%; P = .019). With a 44-month median follow-up, 3-year progression-free survival (PFS) and overall survival for patients with confirmed GZL were 39% and 95%, respectively, vs 58% and 85%, respectively, for reclassified cases (P = .19 and P = .15, respectively). Interestingly, NS grade 2 reclassified patients had similar PFS as GZL consensus-confirmed cases. For prognostication of GZL cases, hypoalbuminemia was a negative factor (3-year PFS, 12% vs 64%; P = .01), whereas frontline cyclophosphamide, doxorubicin, vincristine, and prednisone ± rituximab (CHOP±R) was associated with improved 3-year PFS (70% vs 20%; P = .03); both factors remained significant on multivariate analysis. Altogether, accurate diagnosis of GZL remains challenging, and improved therapeutic strategies are needed.

Objectives To report the clinicopathologic features of monotypic immunoglobulin G4+ (IgG4+) lymphoid and plasmacytic proliferations. Methods Cases were identified from the pathology files. Pathology and clinical materials were reviewed. Results Eleven cases of monotypic IgG4+ proliferations were identified at nodal, orbital, or salivary sites. Six cases (three men, three women; age, 57-94 years) met criteria for lymphoma or plasma cell neoplasia. Most contained frequent Mott cells. Five cases (three men, two women; age, 40-80 years) had restricted proliferations of atypical/monotypic IgG4+ plasma cells in a background of reactive lymphoid hyperplasia or inflammation. Conclusions Monotypic IgG4+ proliferations include lymphomas, plasmacytic neoplasms, and a previously uncharacterized group of proliferations not meeting criteria for conventional hematolymphoid neoplasia. Distinct features included prominent Mott cells and/or monotypic plasma cells within follicles. The proliferations were infrequently associated with IgG4-related disease (IgG4-RD). Our findings raise questions regarding the relationship between clonal IgG4+ proliferations, reactive/inflammatory processes, and IgG4-RD.

The major aim of Session 1 of the 2018 European Association of Hematopathology/Society for Hematopathology Workshop was to collect examples of cutaneous lymphomas, excluding mycosis fungoides/Sezary syndrome, as defined in the current WHO classification of tumours of the haemetopoietic and lymphoid tissues. Overall 42 cases were submitted. These were considered in four main categories: primary cutaneous B cell lymphomas (12 cases), primary cutaneous T cell lymphomas/lymphoproliferations with CD8+/cytotoxic phenotype (12 cases), primary cutaneous CD30-positive lymphoproliferative disorders (15 cases) and primary cutaneous T cell lymphomas/leukaemias with CD4+ phenotype (4 cases). Using these cases as examples, we were able to present the full spectrum of cutaneous lymphoproliferations (excluding mycosis fungoides/Sezary syndrome), including examples of rare, provisional and new entities as listed in the 2017 update of the WHO classification. The findings are summarized in this report with emphasis on differential diagnostic considerations and the importance of clinico-pathological correlation for final subtyping. In presenting these findings we hope to raise awareness of this enigmatic group of neoplasms and to further our understanding of these rare disease entities.

Mantle cell lymphoma (MCL) is characterized by the t(11;14)(q13;q32) translocation resulting in overexpression of cyclin D1. However, a small subset of cyclin D1− MCL has been recognized, and approximately one-half of them harbor CCND2 translocations while the primary event in cyclin D1−/D2− MCL remains elusive. To identify other potential mechanisms driving MCL pathogenesis, we investigated 56 cyclin D1−/SOX11+ MCL by fluorescence in situ hybridization (FISH), whole-genome/exome sequencing, and gene-expression and copy-number arrays. FISH with break-apart probes identified CCND2 rearrangements in 39 cases (70%) but not CCND3 rearrangements. We analyzed 3 of these negative cases by whole-genome/exome sequencing and identified IGK (n = 2) and IGL (n = 1) enhancer hijackings near CCND3 that were associated with cyclin D3 overexpression. By specific FISH probes, including the IGK enhancer region, we detected 10 additional cryptic IGK juxtapositions to CCND3 (6 cases) and CCND2 (4 cases) in MCL that overexpressed, respectively, these cyclins. A minor subset of 4 cyclin D1− MCL cases lacked cyclin D rearrangements and showed upregulation of CCNE1 and CCNE2. These cases had blastoid morphology, high genomic complexity, and CDKN2A and RB1 deletions. Both genomic and gene-expression profiles of cyclin D1− MCL cases were indistinguishable from cyclin D1+ MCL. In conclusion, virtually all cyclin D1− MCLs carry CCND2/CCND3 rearrangements with immunoglobulin genes, including a novel IGK/L enhancer hijacking mechanism. A subset of cyclin D1−/D2−/D3− MCL with aggressive features has cyclin E dysregulation. Specific FISH probes may allow the molecular identification and diagnosis of cyclin D1− MCL.

ObjectiveIgG4-related disease (IgG4-RD) is a heterogeneous, multiorgan condition of unclear aetiology that can cause organ failure. Difficulty recognising IgG4-RD contributes to diagnostic delays. We sought to identify key IgG4-RD phenotypes.MethodsWe used two cross-sectional studies assembled by an international, multispecialty network of IgG4-RD specialists who submitted 765 cases to derive and replicate phenotypic groups. Phenotype groups of disease manifestations and key covariate distributions across the identified groups were measured using latent class analysis.ResultsIn the derivation cohort (n=493), we identified four groups with distinct manifestations: Group 1 (31%), Pancreato-Hepato-Biliary disease; Group 2 (24%), Retroperitoneal Fibrosis and/or Aortitis; Group 3 (24%), Head and Neck-Limited disease and Group 4 (22%), classic Mikulicz syndrome with systemic involvement. We replicated the identification of four phenotype groups in the replication cohort. Compared with cases in Groups 1, 2 and 4, respectively, cases in Group 3 were more likely to be female (OR 11.60 (95% CI 5.39 to 24.98), 10.35 (95% CI 4.63 to 23.15) and 9.24 (95% CI 3.53 to 24.20)) and Asian (OR 6.68 (95% CI 2.82 to 15.79), 7.43 (95% CI 2.97 to 18.56) and 6.27 (95% CI 2.27 to 17.29)). Cases in Group 4 had a higher median serum IgG4 concentration (1170 mg/dL) compared with groups 1–3 (316, 178 and 445 mg/dL, respectively, pConclusionWe identified four distinctive IgG4-RD phenotypes according to organ involvement. Being Asian or female may predispose individuals to head and neck-limited disease. These phenotypes serve as a framework for identifying IgG4-RD and studying its aetiology and optimal treatment.

Introduction Gastrointestinal (GI) involvement by systemic mastocytosis (SM) presents with nonspecific symptoms, and pathologic diagnosis can be difficult when a subtle mast cell infiltrate is present. This series aims to characterize the clinicopathologic features in diagnostically challenging cases. Methods Seven patients with GI biopsies showing an atypical mast cell infiltrate were identified, including 3 consultation cases in which mast cells were initially overlooked. Clinicopathologic characteristics were evaluated. Results Biopsies showed involvement of the large bowel (n=5), small bowel (n=1), or both (n=1) by a wide morphologic spectrum of mast cells, including: bland spindle cells; small cells with irregular nuclei; and medium-sized monotonous cells with abundant pale cytoplasm. The patterns of mucosal involvement included: a polypoid mast cell aggregate (n=1); a confluent subepithelial band of mast cells (n=3); and multifocal aggregates of mast cells (n=3). There were admixed eosinophils with a noticeable lack of plasma cells. Mast cells in all cases showed strong positive staining for CD117 and CD25. All patients fulfilled WHO criteria for SM. On follow-up in 4 cases, none had progression of disease. Conclusions Atypical mast cell infiltrates in the intestine are often subtle and can easily be overlooked. Clues to diagnosis include lamina propria expansion by monotonous cells with pale cytoplasm, admixed eosinophils, and absence of crypt distortion or significant plasmacytic infiltrate. While most patients with GI involvement by SM are symptomatic, a subset remains asymptomatic, and the absence of clinical suspicion of mast cell disease adds to the difficulty in making a diagnosis of SM. This article is protected by copyright. All rights reserved.

Primary mediastinal large B-cell lymphoma (PMBL) is a distinct subtype of diffuse large B-cell lymphoma (DLBCL) that shows overlap with classical Hodgkin lymphoma (CHL) and a favorable prognosis compared to mediastinal gray-zone lymphoma (MGZL). We performed immunohistochemistry on initial diagnostic specimens of 49 cases of uniformly treated PMBL to determine the frequency and clinical significance of expression of antigens commonly seen in CHL and MGZL, along with markers previously shown to be prognostic in DLBCL, not otherwise specified. The median age was 37 years with a female:male ratio of 2.3. After a median follow-up of 78 months, 24% of patients had relapsed or refractory disease and 22% had died; the 5-year PFS was 70%. Variable CD15 expression was seen in 31% of cases, but was not associated with adverse outcome. Hans cell-of-origin, proliferation index, and MYC/BCL2 coexpression were not associated with outcome, while low PDL1 (P = 0.011) and high MUM1 (P = 0.065) staining were each associated with shorter PFS. A biologic risk score (one point each for low PDL1 and high MUM1) stratified patients into three prognostic risk groups for PFS (P = 0.001) and OS (P = 0.032). On separate multivariate models, low PDL1 was independent of R-IPI risk group for PFS (HR 6.0, P = 0.023), as was a biologic risk score of 2 (HR 5.6, P = 0.011). Incorporation of the biologic risk score sub-stratified patients within R-IPI groups for both PFS (P

Primary central nervous system lymphomas (PCNSLs) and primary testicular lymphomas (PTLs) are extranodal large B-cell lymphomas (LBCLs) with inferior responses to current empiric treatment regimens. To identify targetable genetic features of PCNSL and PTL, we characterized their recurrent somatic mutations, chromosomal rearrangements, copy number alterations (CNAs), and associated driver genes, and compared these comprehensive genetic signatures to those of diffuse LBCL and primary mediastinal large B-cell lymphoma (PMBL). These studies identify unique combinations of genetic alterations in discrete LBCL subtypes and subtype-selective bases for targeted therapy. PCNSLs and PTLs frequently exhibit genomic instability, and near-uniform, often biallelic, CDKN2A loss with rare TP53 mutations. PCNSLs and PTLs also use multiple genetic mechanisms to target key genes and pathways and exhibit near-uniform oncogenic Toll-like receptor signaling as a result of MYD88 mutation and/or NFKBIZ amplification, frequent concurrent B-cell receptor pathway activation, and deregulation of BCL6. Of great interest, PCNSLs and PTLs also have frequent 9p24.1/PD-L1/PD-L2 CNAs and additional translocations of these loci, structural bases of immune evasion that are shared with PMBL.

Purpose Breast implant–associated anaplastic large-cell lymphoma (BI-ALCL) is a rare type of T-cell lymphoma that arises around breast implants. The optimal management of this disease has not been established. The goal of this study is to evaluate the efficacy of different therapies used in patients with BI-ALCL to determine an optimal treatment approach. Patients and Methods In this study, we applied strict criteria to pathologic findings, assessed therapies used, and conducted a clinical follow-up of 87 patients with BI-ALCL, including 50 previously reported in the literature and 37 unreported. A Prentice, Williams, and Peterson model was used to assess the rate of events for each therapeutic intervention. Results The median and mean follow-up times were 45 and 30 months, respectively (range, 3 to 217 months). The median overall survival (OS) time after diagnosis of BI-ALCL was 13 years, and the OS rate was 93% and 89% at 3 and 5 years, respectively. Patients with lymphoma confined by the fibrous capsule surrounding the implant had better event-free survival (EFS) and OS than did patients with lymphoma that had spread beyond the capsule (P = .03). Patients who underwent a complete surgical excision that consisted of total capsulectomy with breast implant removal had better OS (P = .022) and EFS (P = .014) than did patients who received partial capsulectomy, systemic chemotherapy, or radiation therapy. Conclusion Surgical management with complete surgical excision is essential to achieve optimal EFS in patients with BI-ALCL.

Although chronic inflammatory disorders of the ocular adnexa are relatively common, their pathogenesis is in many cases poorly understood. Recent investigation suggests that many cases of sclerosing orbital inflammation are a manifestation of IgG4-related disease; however, most patients reported have been Asian, and it is not clear whether the results of studies from the Far East can be reliably extrapolated to draw conclusions about Western patients. We evaluated 38 cases previously diagnosed as orbital inflammatory pseudotumor or chronic dacryoadenitis to determine whether our cases fulfill the criteria for IgG4-RD (IgG4-related dacryoadenitis when involving the lacrimal gland, and IgG4-related sclerosing orbital inflammation when involving orbital soft tissue). Fifteen patients had IgG4-related dacryoadenitis or orbital inflammation. These patients included 9 men and 6 women, aged 24 to 77 years (median, 64 y). Lesions involved orbital soft tissue (8 cases), lacrimal gland (6 cases), and canthus (1 case). In 1 case, focal in situ follicular neoplasia was seen in a background of IgG4-RD. In another case, a clonal IGH gene rearrangement was detected. Four patients with IgG4-RD had evidence of IgG4-RD in other anatomic sites. Five patients, 1 man and 4 women, aged 26 to 74 years (median 50 y) had orbital lesions (2 involving lacrimal gland, 3 involving soft tissue) suspicious for, but not diagnostic of, IgG4-RD. Of 16 patients with IgG4-RD or probable IgG4-RD with information available regarding the course of their disease, 11 patients experienced recurrent or persistent orbital disease. However, no patient developed lymphoma, and no patient died of complications of IgG4-RD. Eighteen patients had lesions not representing IgG4-RD. They included 6 male and 12 female individuals aged 6 to 77 years (median, 47 y). These patients had a variety of diseases, including granulomatosis with polyangiitis (3 cases), Rosai-Dorfman disease (1 case), nonspecific chronic inflammation and fibrosis involving lacrimal gland or soft tissue (12 cases), and others. Clinical and pathologic findings among our patients with IgG4-RD involving the orbit are similar to those previously described in Asian patients. Careful evaluation of histologic and immunophenotypic features and clinical correlation are required to distinguish orbital IgG4-RD from other sclerosing inflammatory lesions in the orbit.

We report four new cases of natural killer-cell enteropathy (NKCE) and similar lymphoproliferative disorders (LPDs), as well as review the literature concerning indolent natural killer (NK)-cell LPDs of the gastrointestinal tract.Pathologic and clinical data were obtained from institutional/referral records.Patient 1 (45-year-old man) had anemia; a small intestinal lesion was endoscopically biopsied. Patient 2 (65-year-old woman) had biliary colic, treated with cholecystectomy. Patient 3 (62-year-old man) had a small colonic polyp, biopsied on routine colonoscopy. Patient 4 (68-year-old man) had presumed Crohn disease; multiple biopsies were performed over more than 10 years. Diagnostic specimens showed atypical infiltrates of Epstein-Barr virus-negative lymphocytes with immunophenotypes suggestive of NK cells. In all cases, there was distortion of glandular architecture but no marked intraepithelial lymphocytosis or necrosis. The patients did not receive therapy for lymphoma and were well on follow-up.These cases support the indolent nature of NKCE and similar LPDs, and they indicate that involvement outside the alimentary canal may occur.

Objectives We report four new cases of natural killer-cell enteropathy (NKCE) and similar lymphoproliferative disorders (LPDs), as well as review the literature concerning indolent natural killer (NK)-cell LPDs of the gastrointestinal tract. Methods Pathologic and clinical data were obtained from institutional/referral records. Results Patient 1 (45-year-old man) had anemia; a small intestinal lesion was endoscopically biopsied. Patient 2 (65-year-old woman) had biliary colic, treated with cholecystectomy. Patient 3 (62-year-old man) had a small colonic polyp, biopsied on routine colonoscopy. Patient 4 (68-year-old man) had presumed Crohn disease; multiple biopsies were performed over more than 10 years. Diagnostic specimens showed atypical infiltrates of Epstein-Barr virus-negative lymphocytes with immunophenotypes suggestive of NK cells. In all cases, there was distortion of glandular architecture but no marked intraepithelial lymphocytosis or necrosis. The patients did not receive therapy for lymphoma and were well on follow-up. Conclusions These cases support the indolent nature of NKCE and similar LPDs, and they indicate that involvement outside the alimentary canal may occur.

Lymph nodes and lymphoid tissue in various extranodal sites can be involved by a variety of reactive processes. In many cases, the histologic changes are nonspecific, and a particular cause cannot be assigned; in other cases, the findings are suspicious for, or even diagnostic of, a certain entity. This chapter focuses on histologically distinctive lymphoid hyperplasias and lymphadenitides and on their differential diagnosis. A number of types of reactive lymphoid hyperplasias can have histologic features that are atypical, distorting the nodal architecture and potentially mimicking a lymphoproliferative disorder. Familiarity with the range of changes that may be seen in reactive lymph nodes can help prevent a misdiagnosis of lymphoma.

The diagnosis of a CD30+ cutaneous infiltrate is often difficult and requires clinicopathologic correlation. To further evaluate this challenge, initial clinical and histopathologic diagnoses were correlated with final clinicopathologic diagnosis in 44 cases with CD30 immunopositivity. Dermatopathologic evaluation confirmed the initial clinical diagnosis in 65% of the suspected benign cases, all cases of suspected lymphomatoid papulosis (LyP), and 72% of clinically malignant cases. In the 25 patients with clinical suspicion for lymphoma, the histopathologic diagnoses included lymphoma in 18, LyP in 2, CD30+ lymphoproliferative disorder (CD30 LPD) in 3 and hypersensitivity reaction in 2 patients. Clinicopathologic correlation led to a change in three cases diagnosed histopathologically as anaplastic large cell lymphoma (ALCL) reclassified as LyP type C, and one patient diagnosed as CD30 LPD clinically evolved as herpes virus infection. Furthermore, five cases reported as CD30 LPD received more specific diagnoses after clinicopathologic correlation (LyP type C in three, and ALCL in two patients). Clinicopathologic correlation is essential in establishing the correct diagnosis of CD30 LPD, in particular the distinction of ALCL from LyP type C. In this setting, the histopathologic diagnosis of CD30 LPD is advisable in the absence of clinical data.

Approximately 30% of patients with follicular lymphoma (FL) transform to a more aggressive malignancy, most commonly diffuse large B cell lymphoma. Rarely, FL transformation results in clinical findings, histology, and immunophenotype reminiscent of B-lymphoblastic leukemia/lymphoma. We report the largest series to date with detailed analysis of 7 such patients. Lymphoblastic transformation occurred on average 2 years after initial diagnosis of FL. Five patients had prior intensive chemotherapy. Two patients developed mature high-grade lymphoma, followed by the lymphoblastic transformation. FL had BCL2 gene rearrangement in 4 of 5 cases. High-grade transformation was accompanied by MYC gene rearrangement (5 of 5). Transformation was characterized by expression of TdT, loss of Bcl6, variable loss of immunoglobulin light chain, and persistence of Pax-5, Bcl2, and CD10. Whole-exome sequencing in 1 case revealed presence of several actionable mutations (CD79B, CCND3, CDK12). FL, aggressive mature B cell lymphoma, and lymphoblastic transformation were clonally related in 6 evaluable cases. After transformation, survival ranged from 1 to 14 months. Four patients died of disease, 2 were in remission after stem cell transplant, and 1 was alive with disease.

Background Pseudolymphomatous folliculitis is a lymphoid proliferation that clinically and histopathologically mimics primary cutaneous extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma). In this study, we assessed the diagnostic value of three immunohistochemical markers, programmed death-1 (PD-1), CD1a and S100. Methods We evaluated 25 cases of cutaneous lymphoid proliferations with established diagnoses, including 9 patients with pseudolymphomatous folliculitis, 11 with MALT lymphoma, and 5 with cutaneous lymphoid hyperplasia (CLH). The clinical, histopathologic and immunohistochemical characteristics were reviewed and three major characteristics assessed: (a) proportion of T cells expressing PD-1, (b) pattern of expression of CD1a by dendritic cells and (c) pattern of expression of S100 by dendritic cells. Results We found pseudolymphomatous folliculitis to have a significant increase in PD-1+ T cells compared with MALT lymphoma (p < 0.0001). The pattern of CD1a staining is also informative: MALT lymphoma is significantly more likely to demonstrate a peripheral concentration of CD1a+ dendritic cells around lymphoid nodules than pseudolymphomatous folliculitis (p < 0.0003) or CLH (p < 0.05). Pseudolymphomatous folliculitis demonstrates an interstitial distribution of CD1a+ cells more often than MALT lymphoma (p < 0.04). S100 staining was not a helpful discriminator. Conclusions Histopathologic factors including PD-1 and CD1a staining patterns may allow for more certainty in distinguishing lymphoid hyperplasia, including pseudolymphomatous folliculitis, from MALT lymphoma.

Immunohistochemistry is a powerful tool for the diagnosis and subclassification of hematolymphoid neoplasms. However, the expression of certain markers is not always as expected, and unusual patterns of staining can lead to misdiagnosis. CD20 and CD3 are our most commonly used markers for identification of B cells and T cells, respectively, and they almost always yield reliable, specific staining. This discussion focuses on diagnostic pitfalls related to the use of immunohistochemistry for CD20 and CD3 in hematopathology, and specifically on diagnostic challenges that arise when (1) CD20 is not expressed in B-cell lymphomas, when (2) CD20 is expressed in plasma cell neoplasms and T-cell lymphomas, and when (3) CD3 is expressed in B-cell lymphomas and Hodgkin lymphoma.

To report the clinicopathologic features of monotypic immunoglobulin G4+ (IgG4+) lymphoid and plasmacytic proliferations.Cases were identified from the pathology files. Pathology and clinical materials were reviewed.Eleven cases of monotypic IgG4+ proliferations were identified at nodal, orbital, or salivary sites. Six cases (three men, three women; age, 57-94 years) met criteria for lymphoma or plasma cell neoplasia. Most contained frequent Mott cells. Five cases (three men, two women; age, 40-80 years) had restricted proliferations of atypical/monotypic IgG4+ plasma cells in a background of reactive lymphoid hyperplasia or inflammation.Monotypic IgG4+ proliferations include lymphomas, plasmacytic neoplasms, and a previously uncharacterized group of proliferations not meeting criteria for conventional hematolymphoid neoplasia. Distinct features included prominent Mott cells and/or monotypic plasma cells within follicles. The proliferations were infrequently associated with IgG4-related disease (IgG4-RD). Our findings raise questions regarding the relationship between clonal IgG4+ proliferations, reactive/inflammatory processes, and IgG4-RD.

Primary bone (PB) diffuse large B-cell lymphoma (DLBCL) is rare and has a favorable prognosis, but the underlying biological mechanisms remain unknown. In this study we analyzed the clinicopathologic features of 160 patients with PB-DLBCL in comparison with 499 nonosseous DLBCL. Compared with patients with nonosseous DLBCL and secondary involvement of bone by DLBCL, PB-DLBCL patients less frequently had elderly age, B-symptoms, elevated serum lactate dehydrogenase levels, and high International Prognostic Index at diagnosis, more frequently had germinal center (GC) subtype (approximately 90%) and complete remission, and had significantly better survival. The 5-year progression-free and overall survival rates of PB-DLBCL patients were 80% and 93%, respectively, superior to both GC B-cell-like (GCB) and activated B cell-like subtypes of DLBCL. Further stratifying nonosseous DLBCL cell-of-origin subtypes by clinical factors showed that PB-DLBCL had similar survival rates as the centrocyte-origin (CC) subtype of DLBCL-GCB classified by the B-cell-associated gene signature algorithm. To better understand the favorable outcome of PB-DLBCL patients, gene expression profiling and microRNA profiling were performed in a small subset of PB-DLBCL. The gene expression profiles of PB-DLBCL resembled those of nonosseous DLBCL-GCB-CC, but were distinct from other DLBCL cell-of-origin especially the centroblast-origin (CB) subtype. Compared with DLBCL-GCB-CB, PB-DLBCL and DLBCL-GCB-CC also had much higher levels of miR-125a-3p, miR-34-3p, and miR-155-5p, and significantly lower levels of miR-17-5p and miR-17-3p. These results demonstrated that PB-DLBCL is clinically distinct, and the cell-of-origin of PB-DLBCL stems from centrocytes in the GC, that are biologically attributed for the favorable prognosis of PB-DLBCL.