ERBB2 and ductal breast carcinoma in situ: Using the Carolina Breast Cancer Study, we restricted analyses to Luminal A cases, which comprise a majority of DCIS cases[14], because breast cancer represents multiple diseases (i.e. Luminal A, Luminal B, Basal-like, HER2-enriched) with distinct risk factors[15–17] and the frequency of each subtype varies between DCIS and invasive breast cancers due to length bias.[18–21] Second, the vast majority of DCIS are detected by mammography, while invasive breast cancers are more often symptomatic.