Anaplastic large cell lymphoma: unusual clinical and pathologic findings: A report of the 2023 SH-EA4HP Lymphoma Workshop.

Anaplastic large cell lymphoma (ALCL) cases were discussed at the 2023 Society of Hematopathology/European Association for Haematopathology workshop held on November 9-11, 2023, in Houston, Texas. This session focused on the clinical and pathologic spectrum of 3 types of ALCL: anaplastic lymphoma kinase (ALK)-positive, ALK-negative, and breast implant associated (BIA). Cases of primary cutaneous ALCL were excluded because they were included in another session. Although the diagnosis of ALCL is often straightforward, the 42 submitted cases encompassed unusual clinical presentations, morphologic variants, and atypical immunophenotypes, exemplifying potential difficulties and challenges in establishing the diagnosis of ALCL. Distinguishing ALCL from CD30-positive peripheral T-cell lymphoma, not otherwise specified, or classic Hodgkin lymphoma was discussed. In patients with a previous history of mycosis fungoides and other T-cell lymphoma/leukemia, the differential diagnosis of a CD30-positive T-cell lymphoma mimicking ALCL (mycosis fungoides transformation vs de novo ALCL) was also discussed. In patients with suspected BIA-ALCL, it is critical to properly handle the periprosthetic fluid when the disease first presents and the capsule at the time of initial capsulectomy to make a correct diagnosis and pathologic staging because a missed diagnosis may lead to disease progression. Comprehensive immunohistochemical analysis; fluorescence in situ hybridization for DUSP22, TP63, or JAK2 rearrangement; assessment of clonality of the T-cell receptor and immunoglobulin genes; and sequencing for mutations were performed as part of the workup of the submitted cases, particularly on ALK-negative ALCL cases, emphasizing the importance of ancillary testing in establishing the diagnosis.