The study of the underlying pathological context, the cytogenetical and TCR-γ clonality analyses and the search of mutations in the SH2 domain of STAT3 and STAT5b should help to distinguish LGL leukemia or other malignant lymphomas from non clonal CD8+ T-cell expansions. The gene discussed is TRGC1; the disease is T-cell large granular lymphocyte leukemia.