Chen et al. (2002) showed through in vitro tests with breast cancer cells that high doses of As2O3 reduce cell survival, whereas low doses inhibit ERα gene expression, which is restored 24 h after the removal of arsenide. Da Silva et al. (2017) found that mice injected subcutaneously with ATO for 5 consecutive weeks had downregulated levels of AR expression in mesenchymal and epididymal epithelial cells. Rosenblatt et al. (2009) found that ATO downregulates AR expression levels and inhibits AR transcriptional activity in prostate cell lines (PC3, LNCap, and LAPC4 cells). The gene discussed is AR; the disease is breast cancer.