AR and cancer: Tumor-specific regulation of APA, leading to the overexpression of oncogenes or the inactivation of tumor suppressors, is widespread in cancer.2–8 In prostate cancer, APA of AR mRNAs can promote the synthesis of constitutively active AR variants, including AR-variant 7 (AR-V7),9 and cell cycle progression of prostate cancer cells can be enhanced through Sam68/XRN2-dependent APA events.10