CDKN1B and multiple endocrine neoplasia: Importantly, low protein levels of p27 constitute a poor prognosis marker for several types of cancer (Chu et al., 2008) and germline mutations of the p27 gene (also known as CDKN1B) are responsible for a subset of human multiple endocrine neoplasia (MEN) syndromes, notably characterized by pituitary tumors (Marinoni and Pellegata, 2011; Vandeva et al., 2010).