RB1 and small cell lung carcinoma: Multifocal lung tumors of multiple histologic subtypes developed in p16-deficient mice including SCLC which were never seen or reported in mice with RB1 or p16 loss alone or in RB1/p16-proficient controls (Table 1).11, 24, 31, 32, 33 Aggressive sarcomatoid carcinoma with chest wall invasion and metastatic nodules involving the diaphragm developed in a p16-deficient mouse that was morphologically indistinguishable from human sarcomatoid NSCLC and the subcutaneous tumors that developed from RB1/p16-deficient cells (Figures 6a–e).