ESR1 and ductal breast carcinoma in situ: Although ER-status has been incorporated as one of the major pathologic factors, along with comedonecrosis, in a clinical score system for predicting DCIS recurrence [24], the results of two clinical studies, UKANZ and NSABP B-24, suggest that ER status is a weakly prognostic biomarker for local recurrence, but it is a strong predictor of response to endocrine therapy to reduce local recurrence.