REXO2 and breast cancer: Notably, among those genetic alteration events whose loss enhances CDK4/6i sensitivity, CDK6, CCND3, CCNE1 and E2F3 were frequently amplified in the genomes of breast cancer patients (Supplementary Fig. 1d–i), whereas among the genes whose loss promotes resistance, RB1, REXO2, PPP2R2A and STT3A were mainly depleted (Supplementary Fig. 1j–o).