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Hepatosplenic T-cell lymphoma is a rare, aggressive T-cell lymphoma, characterized by hepatosplenic sinusoidal infiltration of monotonous, medium-sized, nonactivated cytotoxic T cells, usually of γ/δ T-cell receptor type. Hepatosplenic T-cell lymphoma occurs more frequently in immunocompromised patients, especially in those receiving long-term immunosuppressive therapy. Patients usually manifest hepatosplenomegaly without lymphadenopathy. The bone marrow is also involved in two-thirds of cases and is often accompanied by circulating lymphoma cells, which, along with anemia and thrombocytopenia, may raise suspicion for acute leukemia. The differential diagnosis includes aggressive natural killer-cell leukemia, T-large granular lymphocytic leukemia, T-lymphoblastic leukemia, enteropathy-associated T-cell lymphoma type II, primary cutaneous γ/δ T-cell lymphoma, other peripheral T-cell lymphomas, myelodysplastic syndrome, and infectious mononucleosis. The diagnosis is usually established from the combination of clinical findings, histologic features, and immunophenotype, although cytogenetic/molecular studies are occasionally needed. Hepatosplenic T-cell lymphoma exhibits a dismal clinical course with a poor response to currently available therapies. [ABSTRACT FROM AUTHOR]

Blastic plasmacytoid dendritic cell neoplasm is a rare entity grouped with the acute myeloid leukemia-related precursor neoplasms in the 2008 World Health Organization classification. It was previously postulated to originate from natural killer cells, T cells, or monocytes but is now believed to arise from the plasmacytoid dendritic cell. The pathogenesis of blastic plasmacytoid dendritic cell neoplasm is not well understood, although the neoplasm demonstrates frequent deletion of tumor suppressor genes, including RB1, CDKN1B, CDKN2A, and TP53. Blastic plasmacytoid dendritic cell neoplasm is a clinically aggressive tumor that often initially presents as cutaneous lesions and subsequently progresses to bone marrow involvement and leukemic dissemination. It is characterized by enhanced expression of CD56, CD4, and CD123, which can be detected by flow cytometry/immunohistochemistry. The differential diagnoses include myeloid sarcoma/acute myeloid leukemia, T-cell lymphoblastic leukemia/lymphoma, NK-cell lymphoma/leukemia, and some mature T-cell lymphomas/leukemias. Patients usually respond to initial chemotherapy but often relapse. Stem cell transplant may improve survival. [ABSTRACT FROM AUTHOR]

Kikuchi-Fujimoto disease, or histiocytic necrotizing lymphadenitis, is a self-limited condition, characterized by benign lymphadenopathy with associated fevers and systemic symptoms. It most commonly affects adults younger than 40 years of age and of Asian descent. Involved lymph nodes demonstrate paracortical areas of apoptotic necrosis with abundant karyorrhectic debris and a proliferation of histiocytes, plasmacytoid dendritic cells, and CD8+ T cells in the absence of neutrophils. Kikuchi-Fujimoto disease is thought to have 3 evolving phases: proliferative, necrotizing, and xanthomatous. The etiology is unknown, although viruses and autoimmune mechanisms have been proposed. No specific laboratory tests contribute to the diagnosis. Diagnosis requires histopathologic examination and exclusion of other factors by ancillary studies. Non-Hodgkin lymphoma and systemic lupus erythematosus should be ruled out before diagnosis of Kikuchi-Fujimoto disease, given the overlapped clinical and histologic features as well as the different therapeutic approaches. Treatment involves supportive measures, and the symptoms usually resolve spontaneously within 4 months. [ABSTRACT FROM AUTHOR]

Pelger-Huët anomaly is a congenital or acquired abnormality of neutrophil nuclear segmentation. The acquired form may be a result of a clonal myeloid malignancy, such as myelodysplastic syndrome, or may be a secondary nonclonal change related to a variety of underlying causes, including infections and medications. We report a case of a 56-year-old man who developed acquired Pelger-Huët anomaly following liver transplantation while on the immunosuppressive agents tacrolimus and mycophenolate mofetil. These medications have been reported in association with this abnormality, but usually as a single agent or in combination with other drugs. In our case, the Pelger-Huët anomaly may be the result of the combination of these 2 drugs or mycophenolate alone with subsequent desensitization because resolution of the abnormality occurred after a reduction in mycophenolate mofetil dose, and the abnormality did not recur when mycophenolate mofetil was increased to a dose previously associated with Pelger-Huët anomaly during the time that tacrolimus was discontinued. [ABSTRACT FROM AUTHOR]

Context.--In the 2017 revised World Health Organization classification of tumors of hematopoietic and lymphoid tissues, some mature T-cell lymphomas were reclassified and a few new provisional entities were established based on new data from clinical and laboratory studies. T follicular helper cell lymphoma is identified by T follicular helper cell markers. Anaplastic large cell lymphoma, ALK negative, is a better-defined entity based on genetic abnormalities, and breast implant--associated anaplastic large cell lymphoma is recognized as a provisional entity. The gastrointestinal T-cell lymphomas are reclassified, with addition of a new provisional entity, indolent T-cell lymphoproliferative disorder of the gastrointestinal tract, characterized by an indolent clinical course. Objective.--To review the diagnostic approaches to reclassified and newly established entities of mature T-cell lymphomas, focusing on significant immunophenotypic features and molecular genetic abnormalities. Relevant new discoveries after the publication of the 2017 World Health Organization classification are included. Data Sources.--Information from the literature most relevant to the 2017 World Health Organization revised classification and publications after 2016. Conclusions.--Incorporating clinical, morphologic, and immunophenotypic features usually provides sufficient evidence to reach a preliminary diagnosis of mature T-cell lymphoma. Molecular genetic studies can be very helpful for the final diagnosis and classification, especially in challenging cases. Some molecular genetic features have been found in breast implant--associated anaplastic large cell lymphoma, distinct from anaplastic large cell lymphoma, ALK negative. Immunohistochemical staining of 4 markers may enable further subtyping of peripheral T-cell lymphomas. [ABSTRACT FROM AUTHOR]