A substantial body of work supports the concept that Stat5 is critical for PC cell viability in vitro and xenograft tumor growth in vivo [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25], and IST5 has been shown to induce extensive apoptotic death of PC cells, block growth of PC xenograft tumors in mice in vivo [2,3,4,6,7,8,10,14,15,47], and induce apoptotic death in patient-derived clinical PCs ex vivo in 3D tumor explant cultures [10,47]. Here, STAT5A is linked to pachyonychia congenita.