CCND1 and breast cancer: Usually, a gene aberrantly highly expressed in cancer tissues acts as a negative prognostic factor.41, 42 As an oncogene, increased expression of CCND1 has been proven to be an unfavorable prognostic factor in some cancers including gastric adenocarcinoma patients, lung adenocarcinoma patients, oropharyngeal cancer, and pancreatic carcinoma.15, 33, 34, 35 However, in breast cancer, the increased level of CCND1 has been linked to favorable prognosis.43 These results suggested that CCDNI plays a variety of roles in different cancers.