Stat5a/b (Stat5) is critical for growth and progression of solid tumors and hematological malignancies, specifically prostate cancer (PC) [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 Bcr-Abl-driven leukemias [26,27,28,29,30,31,32,33,34,35]. Here, STAT5A is linked to pachyonychia congenita.