ESR1 and breast carcinoma: In another study, Withaferin A treatment of MCF-7 breast cancer cells led to growth cell growth inhibition, cell cycle arrest in G2/M phase, and apoptosis associated with downregulation of ER-α, HSF1, RET and upregulation of phospho-p38 MAPK, p53, and p21 expression (Zhang et al., 2011).