However, Cdkn1b-knockout (KO) mice develop, among other phenotypic abnormalities, ACTH-secreting hyperplasia or adenomas of the pituitary pars intermedia with full penetrance (Fero et al. 1996, Kiyokawa et al. 1996, Nakayama et al. 1996). This evidence concerns the gene CDKN1B and adenoma.