For example, in addition to the pathognomonic alterations of the TCL1 gene, T-cell prolymphocytic leukemia (T-PLL) frequently displays point mutations of JAK1 (6.3% of cases), JAK3 (36.4%), and STAT5B (18.8%) (50). The gene discussed is STAT5B; the disease is T-cell prolymphocytic leukemia.