Early stages of sporadic breast cancer exhibit the loss of cell cycle checkpoint gene p16INK4a via aberrant CpG promoter methylation (61) and nearly 80% of breast tumors also exhibit a decreased expression of another cell cycle inhibitor gene p21/CIP1/WAF1 via elevated methylation of p21/CIP1/WAF1 gene (62). The gene discussed is CDKN1A; the disease is breast neoplasm.