Blood- and bone marrow-based mature T-cell and natural killer cell leukemias and lymphomas: a summary in the series of the 2023 SH/EAHP Workshop.

This session included 51 cases submitted to the workshop "Progress in T- and NK-cell Lymphomas and Leukemias" by the Society for Hematopathology and European Association for Haematopathology under "Blood/Bone Marrow-Based Mature T- and NK-Cell Leukemias/Lymphomas" or "T/NK-cell neoplasms with a Leukemic Presentation." Entities encompassed T-cell prolymphocytic leukemia, T-cell large granular lymphocytic leukemia (LGLL), natural killer (NK)-LGLL/chronic lymphoproliferative disorder of NK cells, adult T-cell leukemia/lymphoma, aggressive NK-cell leukemia, and their mimics. Submitted cases illustrated classic and variant morphology, immunophenotype, and clinical features; the overlaps with reactive T-cell /NK-cell lymphoproliferations; and challenges in differentiating these entities from other T-cell/NK-cell neoplasms with a leukemic presentation. The cases were assessed using a multidisciplinary approach that included advancements in molecular genetics with their potential impact on clinical practice. We used the most recent classifications and summarized the key points relevant to diagnoses and differential diagnoses of respective entities.