CTSK and osteosarcoma: H&E staining of femurs from 6‐month‐old triple‐cKO mice also showed much less expansive osteosarcoma osteoid lesions in the cortical bone compared to that in Ctsk‐Cre;Trp53f/f/Rb1f/f mice (Figure 7B), indicating that inactivation of YAP blocked osteosarcoma progression in the Ctsk‐Cre;Trp53f/f/Rb1f/f mice.