p53 and p18Ink4cact independently in suppressing Cyclin D1-driven tumors: The persistence of a small number of proliferating cells by P49, in Irbp-Cyclin D1, p18Ink4c -/- mice, was important because it led to pineoblastoma by 7-10 months of age in all mice examined (n = 15). The gene discussed is CCND1; the disease is pineoblastoma.