CDKN2A and breast cancer: To assess the impact of cellular senescence on the interaction between RT and P, we harnessed female INK-ATTAC mice, which express a dimerizable form of caspase 8 (CASP8) under the promoter of cyclin dependent kinase inhibitor 2A (Cdkn2a, coding for p16Ink4) [42], as host for endogenous mammary tumors driven by medroxyprogesterone acetate (MPA, M) pellets plus 7,12-dimethylbenz[a]anthracene (DMBA, D) [43] that were allocated to RT, P or their combination in the optional presence of the CASP8 dimerizer AP20187 (Fig. 1A).