E2F1 and breast cancer: Importantly, knockdown of the transcriptional activities of E2F1, MYBL1, and MYBL2 may be considered as the suggested treatment targets to improve prognosis for a subset of breast cancer population with ER(−) or with advanced ER(+) breast cancers who have elevated E2F1, MYBL1 and MYBL2 in their breast tumors.