RB1 and medullary thyroid gland carcinoma: The Scgb1a1 promoter was chosen for these studies to avoid the high incidence of bilateral medullary thyroid carcinomas that develop in mice with Sftpc driven RB1 ablation due to the targeting of a subset of thyroid cells.30 The incidence of spontaneous lung tumors was nearly doubled in p16-deficient mice with tumors having a more aggressive phenotype as indicated by increased cytologic atypia as well as invasive growth and metastases which were not seen in p16-proficient mice (Table 1 and Figures 6c–j).