CDK6 and neoplasm: The tumor makers analyzed included 1) protein 53 or tumor protein 53 (tp53), a gene that is important in multicellular organisms because of its functions as a tumor suppressor and cell cycle regulator; 2) c-myb proto-oncogene (cmyb), a gene important in the control of proliferation and differentiation of hematopoietic progenitor cells; and 3) cyclin D1 (ccnd1), a regulatory subunit for CDK4 or CDK6 and an essential factor for the cell cycle G1/S transition.