CDKN1A and thymus neoplasm: For instance, in MCF-7 cells BaP induces over-expression of many cell cycle genes including TP53 and CDKN1A[39]; arsenate induces thymus atrophy mediated by cell cycle arrest by down-regulating E2F and related genes [65]; 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) makes cell cycle changes in murine fetal liver [66] and Rb loss abrogates cell cycle control and genome integrity to promote liver tumourigenesis [67].