Loss of pRB expression with no association to LOH of the RB1 intragenic markers has been described in breast carcinomas, prostate cancer, and pituitary adenomas, reinforcing the existence of alternative RB1 gene-inactivating mechanisms (Borg et al, 1992; Cooney et al, 1996; Simpson et al, 1999). This evidence concerns the gene RB1 and pituitary gland adenoma.