Ablation of all three RB1 family proteins in the lung epithelium leads to development of neuroendocrine tumorlets that do not progress to SCLC and no NSCL tumors.43 Thus, additional oncogenic events are required for development of the SCLC and NSCL tumors present in RB1/p16-deficient lungs. Here, RB1 is linked to small cell lung carcinoma.