CDKN1A and gonorrhea: p21Cip1 is overexpressed in hormone-secreting PAs, especially in GH-PAs,[34] and no mutations have been observed in the encoding gene.[35] Chesnokova et al[36] reported that p21Cip1 suppressed pituitary tumor growth, which was correlated with hormonal secretion type, and hypothesized that p21Cip1 overexpression accounted for the very low incidence of PCs.