RB1 and breast cancer: Experimental evidence has linked concomitant inactivation of the p53- and the Rb-pathway to lymphoma development and resistance toward cyclophosphamide in mice through prevention of cellular senescence,20 as well as immortalization of keratinocytes.21 While we found concomitant inactivation of the p53- and Rb-functional pathways to be associated with resistance to DNA damaging drugs in breast cancer patients, the mechanism behind this effect has not been elucidated.22