The association between pathologic complete response (pCR) to neoadjuvant chemotherapy for breast cancer and improved relapse-free survival (RFS) and overall survival (OS) outcomes has been documented in multiple clinical trials, single-institution retrospective studies, and a recent pooled analysis of clinical trials.1 This association is strongest when the definition of pCR includes eradication of invasive cancer in both the breast and axilla, and in patients with human epidermal growth factor receptor 2 (HER2)-overexpressing and triple-negative breast cancers.1 In this issue of JAMA Oncology, Mougalian and co-authors2 examine the relative impact of residual disease in the axillary lymph nodes compared to residual disease in the breast on 10-year RFS and OS outcomes in a heterogenous population of 1600 women with operable and locally advanced breast cancer treated with neoadjuvant chemotherapy at a single institution between 1989 and 2007. Pathologic complete response in both the breast and the axilla was seen in only 19% of patients, nearly identical to the 18% reported by Cortazar et al1 in the pooled analysis of clinical trials, in spite of the fact that almost 75% of patients in the study of Mougalian et al2 were treated with an anthracycline and a taxane. Additionally, pCR in the axilla was seen in a minority of women in the overall study population (28%), but a striking 67% of the 153 HER2-positive patients receiving HER2-directed therapy had an axillary pCR. Patients with pCR in both the breast and axilla had 10-year OS of 90% compared with 72% for those with axillary pCR and residual breast disease (P < .001), and 10-year OS for those with residual axillary disease and breast pCR was 66% compared with 56% for those with residual disease in both the breast and axilla (P = .02), indicating that any residual tumor, regardless of location, has a significant negative effect on prognosis. In multivariable models, residual disease in the axilla or the breast was a significant predictor of an increased risk of recurrence and death.
Morrow M. Parsing Pathologic Complete Response in Patients Receiving Neoadjuvant Chemotherapy for Breast Cancer. JAMA Oncol. 2016;2(4):516-517. doi:10.1001/jamaoncol.2015.4919