RB1 and breast cancer: pRb, regulating the transition between G1/G0- and S-phase in the cell cycle, has a key role executing cell cycle arrest in response to DNA damage.14,15 While conflicting evidence has linked RB1 mutations to lack of, as well as an improved response to chemotherapy;16,17 previously we reported mutations in RB1 to be associated with a poor response to anthracyclines and mitomycin in breast cancer.18,19