PIK3CA and breast cancer: In relation to this observation, BEZ235, a dual inhibitor of PI3K and mTOR, has previously been reported to downregulate p-53BP1 (S25) and 53BP1 foci induced by the poly (ADP-ribose) polymerase inhibitor (PARPi) olaparib in breast cancer type 1 susceptibility protein (BRCA1)-mutant breast cancer cells [374].