ESR1 and breast cancer: One such study was conducted by Yao et al. on human breast cancer cell lines (MDA-MB-231—estrogen receptor-negative and MCF7—estrogen receptor positive), where they showed that ligand activation and/or overexpression of PPARβ/δ inhibits the relative carcinogenicity of breast cancer and provides further support for the development of PPARβ/δ ligands to specifically inhibit breast carcinogenesis [160].