The Presence of an In Situ Component on Pre-Treatment Biopsy Is Not Associated with Response to Neoadjuvant Chemotherapy for Breast Cancer

SIMPLE SUMMARY: Identifying markers predictive of response and resistance to neoadjuvant chemotherapy (NAC) has become a major research objective. Ductal carcinoma in situ (DCIS) is associated with invasive disease in more than half of invasive breast cancer cases. It is generally assumed that DCIS does not respond to NAC, but the effect of chemotherapy on in situ components has been little studied. We assessed the predictive value of the presence of an in situ component on pre-NAC biopsy on pathological complete response (pCR) in a real-life cohort of patients treated by NAC. We included 1148 patients; 44% of tumors were luminal (n = 508), 31% triple negative breast cancer (TNBC) (n = 359) and 24% HER2-positive (n = 281). DCIS was found in 225 samples (19.6%) before NAC. The presence of a DCIS component on pre-NAC biopsy was not associated with pCR and did not seem to be a critical factor for the prediction of response to NAC. ABSTRACT: A ductal in situ (DCIS) component is often associated with invasive breast carcinoma (BC), and its effect on response to treatment is unknown. We assessed the predictive value of the DCIS component for pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC). We analyzed a cohort of 1148 T1–3NxM0 breast cancer (BC) patients treated by NAC at Institut Curie between 2002 and 2012. The presence of a DCIS component was retrospectively recorded from both the pre-NAC biopsy pathological report and surgical specimens. We included 1148 BC patients treated by NAC for whom pre- and post-NAC data concerning the in situ component were available. DCIS was present before NAC in 19.6% of the population. Overall, 283 patients (19.4%) achieved pCR after NAC. There was no significant association between the presence of DCIS on pre-NAC biopsy and pCR. In a multivariate analysis including subtype, tumor size, grade, mitotic index, and Ki67 index, only BC subtype (luminal/TNBC/HER2-positive) and Ki67 were significantly associated with pCR. The presence of a DCIS component on pre-NAC biopsy is not associated with pCR and does not seem to be a critical factor for predicting response to NAC.