Tumor Biology Predicts Pathologic Complete Response to Neoadjuvant Chemotherapy in Patients Presenting with Locally Advanced Breast Cancer

Neoadjuvant chemotherapy (NAC) is used to convert patients with inoperable locally advanced breast cancer (LABC) to operability, but has not traditionally been used to avoid mastectomy or axillary dissection in this subset. The purpose of this study was to determine the rates of pathologic complete response (pCR) in LABC patients, and identify factors predictive of pCR to determine if responding patients might be suitable for limited surgery. From 2006 to 2016, 1522 patients received NAC followed by surgery; 321 had advanced disease in the breast (cT4) and/or in the nodes (cN2/N3). pCR rates were assessed by T and N stage, and receptor subtype. Of 321 LABC patients, 223 were cT4, 77 were cN2, and 82 were cN3. Forty-three percent were hormone receptor (HR) positive/human epidermal growth factor receptor 2 (HER2) negative (HR+/HER2-), 23% were triple negative, and 34% were HER2+. The overall pCR rate was 25% and differed by receptor subtype (HR+/HER2- 7%, triple negative 23%, HER2+ 48%; p < 0.001). Breast pCR occurred in 27% of patients and was similar in T4 versus non-T4 disease (29% vs. 22%; p = 0.26). Nodal pCR was achieved in 38% of cN+ patients and did not differ by nodal stage (cN1 43%, cN2 36%, cN3 32%; p = 0.23). Nodal pCR was significantly more common than breast pCR (p = 0.014) across all tumor subtypes. Receptor subtype was the only predictor of overall pCR (p < 0.001). In patients with LABC, pCR after NAC was seen in 25%, and did not differ by T or N stage. Tumor biology, but not extent of disease, predicted pCR. Studies assessing the feasibility of surgical downstaging with NAC in LABC patients are warranted.