STAT5B and T-cell large granular lymphocyte leukemia: Depending on the immunophenotype of the mutated clone, the presence of STAT5b mutations in the same hotspot positions represents a signature of aggressive clinical course with a poor prognosis in aggressive CD8+ T-LGLL patients (28), while it is devoid of negative prognostic significance in CD4+ T-LGLL and Tγδ LGLL patients (15, 29, 53).