Overall the frequency of STAT5B mutations in our series is lower than that reported by others, not only among TCD4+ (15–55%), but also among TCD8+ (0–25%) and Tγδ+-LGLL cases (19%), where it has been associated with a worse prognosis [11,20,25,28,30]. This evidence concerns the gene STAT5B and T-cell large granular lymphocyte leukemia.