CCNE1 and pituitary gland adenoma: Moreover, it has also been reported that up-regulation of cyclin E (using a transgene construct under the control of the POMC promoter, Tg-PCE) and knockout of p27 (Cdkn1b−/−) in the Tg-PCE/Cdkn1b−/−mouse model, leads to increased pituitary adenoma incidence and frequency (Roussel-Gervais et al., 2010) and that p27 and p18 mediate two separate pathways to collaboratively suppress tumourigenesis (Franklin et al., 1998).