ERBB2 and ductal breast carcinoma in situ: In clinical trials, HER2-positive DCIS tends to recur in situ, while HER2-negative DCIS has a lower recurrence rate.19,292,296–298 Based on these findings, it was supposed that the majority of IDC cases may arise from HER2-negative DCIS (or the HER2-negative subclone of DCIS in cases of heterogeneous HER2 expression).