Regarding endocrine therapy resistance, a previous study using an MCF7-derived tamoxifen-resistant cell line suggests that GAS5 acts as a ceRNA by sponging miR-222 and upregulates PTEN, which is a target of miR-222 and weakens the tamoxifen resistance of breast cancer cells (Figure 4) [102]. The gene discussed is GAS5; the disease is breast cancer.