TP53 and small cell lung carcinoma: Somatic inactivation of Rb1 and p53 using intratracheal injection or intubation of mice with adenovirus-Cre leads to the development of SCLC-like tumors34, whereas mice carrying germline deletion of one Rb1 allele and both p53 alleles (Rb1 + /−p53 − /−) develop a variety of primary tumors of neuroendocrine origin as well as focal bronchial neuroendocrine cell hyperplasia51, showing the critical importance of these factors in preventing transformation and growth of neuroendocrine cells.