Presence of STAT3 mutations in T-LGLL is associated with a worse prognosis (vs. STAT3 wild-type cases), due to a higher frequency of cytopenias (i.e., neutropenia, anemia and to a lesser extent also thrombocytopenia), and other diseases related to dysregulation of T-cell–mediated immunity, such as acquired pure red cell aplasia and rheumatoid arthritis, among other autoimmune and inflammatory diseases, and a higher prevalence of (second) tumors (56). The gene discussed is STAT3; the disease is pure red-cell aplasia.