Comparing tumors with chromosome 11 loss and cytogenetically stable tumors confirm the direct downregulation of the genes in this chromosome, including important tumorigenesis related genes such as ATM, CHEK1, and EMSY that are involved in DNA repair, as well as the pituitary tumor-related genes MEN-1 and AIP (both at chromosome 11.q13). Here, CHEK1 is linked to pituitary tumor.