RB1 and pituitary tumor: To date, homologous deletions of 10 different genes, which are Men1, Cdkn1b, Prkar1a, Rb, Cdkn2b (encoding p19), Drd2, Cdkn2c (encoding p18), Aip, Prl and Prlr, have been reported to yield mouse knockout models for pituitary tumours.