USP15 and cancer: USP15 is a widely expressed deubiquitylase in cancers and its copy number gains have been reported in glioblastoma, breast, and ovarian cancers.29 The proposed targets for USP15 include TGF receptor I and its downstream receptor‐regulated SMAD,30 p53,31 topoisomerase II (TOP2A),29 BRCA1 associated RING domain 1 (BARD1),32 etc. The diverse targets of USP15 suggest that its activity must be tightly regulated and direct within cells.