No allelic loss of Rb was seen in a study of 12 human pituitary tumors, including one corticotroph microadenoma and one macroadenoma (53), but among 13 highly invasive human pituitary adenomas or metastatic carcinomas tumors, all showed loss of Rb, suggesting a preference for loss of Rb in more aggressive corticotroph tumors (55). This evidence concerns the gene RB1 and pituitary tumor.