CDKN1A and breast cancer: VPA decreases cell viability through arresting of the cell cycle in G1 or sub-G1 phases, induction of p21 protein expression and apoptosis by upregulation of Bak, downregulation of Bcl-2 expression, increasing Bax/Bcl-2 ratio, and, as a consequence, decreasing telomerase activity in estrogen-positive MCF7 BC cells.