Pathologic complete response of DCIS to neoadjuvant systemic therapy in HER2-positive invasive breast cancer patients

A ductal carcinoma in situ (DCIS) component can be present in HER2-positive invasive breast cancer (IBC). A retrospective study in The Netherlands found that among women undergoing neoadjuvant systemic therapy (NST) and surgery for IBC, a DCIS component was present in the pre-NST biopsy of 25.1% of patients, and pathologic complete response of DCIS to NST was seen in 52% of these patients. Complete response of DCIS occurred more frequently in case of complete response of IBC (63.4% versus 33.8%; p<0.001). ER-negative IBC and more recent year of diagnosis were associated with DCIS response.