The mice with Rb1, p53, and Rbl2 deletions (Rb/p53/Rbl2 mice) developed many more tumors than those with only Rb and p53 deletions (Rb/p53 mice); these drastic changes in tumor incidence and latency clearly indicate that Rbl2 is a potent tumor suppressor in SCLC development. This evidence concerns the gene TP53 and small cell lung carcinoma.