ESR1 and osteosarcoma: Four ER-positive cell lines in line with the four estrogen-sensitive tissues characterized in the OVX rats, including human breast cancer MCF-7 cells, endometrial cancer Ishikawa cells, neuroblastoma SHSY5Y cells, as well as osteosarcoma MG-63 cells, were employed to investigate the estrogenic activities of RD in vitro.