In most human tumors, the G1/S checkpoint is lost, for example, by loss of pRB or the CDK inhibitor p16INK4A, or by overexpression of cyclin D1 (Ho & Dowdy, 2002) and insensitivity to antigrowth signals is a hallmark of tumor cells (Hanahan & Weinberg, 2000). The gene discussed is CCND1; the disease is neoplasm.