RB1 and sarcoma: This second nonmelanoma tumor is likely caused by inactivation of both rb1 and tp53 in the muscle, as we used ubiquitous Cas9 in our studies, and this combination is commonly found in sarcomas (Cerami et al., 2012; Gao et al., 2013; Gonin-Laurent et al., 2007; Pérot et al., 2010; Stratton et al., 1990).