CO14 | A combined immunophenotypic and molecular approach to differentiate T-CUS, low-count T-LGLL and T-LGLL

Introduction. The identification of small T-cell clones sharing overlapping immunophenotypic and molecular features has blurred the distinction between reactive and neoplastic proliferations, including T-cell Clones of Uncertain Significance (T-CUS), Low-Count (LC) T-cell Large Granular Lymphocyte Leukemia (T-LGLL) and full blown T-LGLL. T-LGLL is a chronic clonal disorder of cytotoxic T lymphocytes often associated with neutropenia and activating STAT mutations. Traditionally, arbitrary thresholds (500/1,000 LGL/µL) separate indolent T-CUS and symptomatic LC T-LGLL from full blown T-LGLL. This study challenges numerical cut-offs and proposes an integrated approach combining immunophenotypic, molecular and clinical data to better define T-cell proliferations.Methods. A cohort of 110 patients was consecutively enrolled and classified, according to clonal size and clinical features, as full blown T-LGLL (n=50; LGL>1,000/µL), LC T-LGLL (n=20; LGL≤1,000/µL and ANC