Interestingly, STAT5b mutations were present only in CD4+ T-LGL leukemia patients, confirming the data reported by Andersson et al [13], although with a lower incidence of 15.2% in CD4+ T-LGL leukemia (5 out of 33 patients) compared to 55% frequency reported by others, likely because of the different number of patients studied (33 versus 11). The gene discussed is CD4; the disease is T-cell large granular lymphocyte leukemia.