Jiang et al. found that miR-503 downregulation promotes proliferation, migration, and invasion of esophageal squamous cell carcinoma (ESCC) cells by targeting cyclin D1 [14]; Long et al. found that miR-503 inhibits human breast cancer cell proliferation by suppressing cyclin D1 expression (20); Xu et al. [21] found that miR-503 suppresses endometrioid endometrial cancer cell proliferation and cycle progression by negatively regulating cyclin D1. The gene discussed is CCND1; the disease is breast cancer.