In vitro selective inhibition of STAT5B [3] with pimozide showed specific and profound decreased cell proliferation in the cell lines expressing mutated IL2G-JAK-STAT (IL2RG, JAK1, JAK3, and STAT5B mutations) genes as opposed to other inhibitors of this axis such as tofacitinib, whose use didn’t result in selective tumor cells killing. The gene discussed is STAT5B; the disease is neoplasm.