For example Men1+/− mice develop PAs but not carcinomas;50 transgenic mice overexpressing cyclin D1 develop adenomas but not carcinomas;51Rb+/− mice develop medullary thyroid carcinomas and pituitary adenocarcinomas but not PCs;52 and Men1+/−/Rb+/− mice developed pituitary, thyroid and pancreatic islet hyperplasia, but not PCs.52 These findings indicate that loss of RB expression and increase of cyclin D1 expression may not be required for PC development in the mouse, and are consistent with our observations that RB and cyclin D1 expression were not altered in the APAs of Cdc73+/− mice. This evidence concerns the gene CDC73 and medullary thyroid gland carcinoma.