ERBB2 and ductal breast carcinoma in situ: Others also have reported that post-NAC MRI appears to be less accurate in ER+ tumors and most accurate in Tneg or Her2+ tumors and that pre-NAC tumor size and response also impact accuracy.34–37 Although some have reported the highest accuracy of MRI for Her2− disease, not knowing HR status and differences in rates of traztuzumab use could potentially account for the disparate results.38 Benign proliferative processes can enhance on MRI and are difficult to differentiate from low-grade, ER+ DCIS lesions.