CCND1 and breast cancer: The reason for recurrences of breast cancer is that a small number of tumor cells resist the effects of adjuvant therapy and then proliferate in local or distant region, and this phenomenon exhibits cyclin D1‐CDK4 dependent proliferation.42 Previous studies showed that Cyclin D1 and D3 are overexpressed in primary invasive breast cancers and human breast cancer cell lines.43 Some studies found CCND1 downregulation have no effect on cancer cell proliferation, which confused many researchers.