ESR1 and breast cancer: Since breast cancer has become the most diagnosed type of cancer in women, especially in Malaysia and generally, worldwide, we aim to investigate the in vitro cytotoxic and anti-metastatic effects of flavokawain A on two types of breast cancer cell lines, MCF-7 and MDA-MB231.Both MCF-7 and MDA-MB231 are well-established breast cancer cell lines but they differ in several aspects including, the p53 status, estrogen receptor status and invasiveness [13].