In a more detailed study [41], whereas the mutation of ERRF was not as frequent as expected, ERRF expression was frequently elevated in breast cancer compared to normal tissues, ERRF expression positively correlated with ER and PR status but negatively correlated with ERBB2 status, and knockdown of ERRF expression reduced tumor growth of ER and PR-positive breast cancer cells [41]. This evidence concerns the gene ESR1 and breast cancer.