CCND1 and breast cancer: Of note, cyclin D1 and E1 both correlated with better outcome, either singly or clustered; this finding may seem counterintuitive as CCND1 is a weak oncogene, but is in line with earlier studies showing that over-expression of cyclin D1 is in fact associated with favorable outcomes in breast cancer, both in terms of prognosis and response to endocrine treatment [28, 29].