Noncutaneous cytotoxic T-cell lymphomas: Recent advances and emerging concepts: A report of the 2023 Society of Hematopathology/European Association for Haematopathology T-cell lymphoma workshop.

Objectives: To review and discuss cases submitted to the 2023 Society of Hematopathology/European Association for Haematopathology workshop session entitled "Non-cutaneous Cytotoxic T-cell Lymphomas Including Hepatosplenic T-cell Lymphoma and Intestinal T-cell Lymphomas.

Methods: A total of 45 cases were submitted by various contributors. These cases included clinicopathologic, immunophenotypic and molecular data.

Results: Cases submitted included 12 hepatosplenic T-cell lymphoma (HSTCL) and 22 intestinal T or NK cell lymphomas or lymphoproliferative disorders (LPD) of various types. The latter group included 12 monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL), 4 indolent NK-cell LPD of the gastrointestinal (GI) tract, 3 indolent (clonal) T-cell lymphoma of the GI tract, 1 refractory celiac disease type 2, 1 enteropathy-associated T-cell lymphoma and 1 intestinal T-cell lymphoma not otherwise specified. There were also 11 miscellaneous cases that did not readily fit into well known diagnostic categories but raised questions about diagnostic criteria or biology or which elucidated aspects of differential diagnosis.

Conclusions: The cases submitted were instructive and helped to further characterize and, in some cases, expand these entities. We suggest that HSTCL is a disease with well recognized clinicopathologic features and genetic features. Patients were older than is reflected in the literature. The cases of MEITL in this workshop came mostly from western and/or in industrialized nations. SETD2 mutation or loss of H3K36me3 by immunohistochemistry as a surrogate for this mutation is very common and a helpful diagnostic tool in MEITL. A surprising finding was that some patients with NK-cell LPD of the GI tract exhibited aggressive clinical features including 1 patient who had disease dissemination to the lungs and bile duct.