In the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-24 study, CBTR was shown to occur more often in patients with estrogen receptor (ER)-positive DCIS than in those with ER-negative DCIS (8.9 vs. 5.6 %) [8], suggesting that the expression of hormone receptors (HRs) by DCIS may predict subsequent contralateral breast cancer [16]. Here, ESR1 is linked to ductal breast carcinoma in situ.