Inactivating STAT5B germline mutations (Bhattacharya et al, 2022; Hwa, 2021; Rajala et al, 2013) have been associated with GH insensitivity (Laron syndrome) and immune pathology, while activating somatic mutations (Bhattacharya et al., 2022; Kiel et al, 2014; Kontro et al, 2014; Rajala et al., 2013) have been identified in patients with T cell large granular lymphoblastic leukemia (T-LGLL) (Bhattacharya et al., 2022; Kiel et al., 2014; Kontro et al., 2014; Rajala et al., 2013) and T-cell prolymphocytic leukemia (T-PLL) (Kiel et al., 2014) . This evidence concerns the gene STAT5B and T-cell prolymphocytic leukemia.