ESR1 and breast cancer: According to Osuna et al. in 2019 [52], the downregulated expression of ERα in osteosarcoma patients may be due to promoter methylation and in osteosarcoma cell lines, the expression of ERα cannot be detected in three osteosarcoma cell lines, including 143B, MG63, and U2OS by Western blot using MCF7 breast cancer cell line as positive control.