T and NK lymphoblastic leukemia/lymphoma: Report from the 2023 SH/EAHP Workshop

Objectives The 2023 Society for Hematopathology/European Association for Hematopathology Workshop addressed advancements in the diagnosis and classification of T- and natural killer (NK)-cell lymphomas/leukemias. Methods Session 8 of the workshop collected a diverse set of 38 cases of immature T- and NK-cell lymphoma/leukemias, as well as acute leukemia of ambiguous lineage (ALAL) and other miscellaneous cases, including indolent T-lymphoblastic proliferations. Results Twenty patients with T-lymphoblastic leukemia/lymphoma (T-LBL/L) and 3 patients with early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) presented at a median age of 21.5 years. Male sex was predominant (70% of all cases), with 40% having a mediastinal mass. Cases (60%) were negative for both CD34 and TdT. In addition, 7 ALAL and 3 mixed phenotype acute leukemia, T/myeloid subtypes were submitted with a median presenting age of 16 (range, 11-56) years, and most patients (67%) frequently showed adenopathy or splenomegaly. A single case of NK acute lymphoblastic leukemia was also submitted. Conclusions This session highlighted unusual T-LBL/L cases with expression of cytotoxic markers, γ/δphenotype, a more mature immunophenotype, and ALAL that are challenging to classify. Among T-ALL cases, interesting relapse changes were identified, with 1 patient developing a mature NK-cell phenotype. Patients with ALAL presented in an unusual setting of prior therapy or a germline mutation.