Relationship Between Breast and Axillary Pathologic Complete Response in Women Receiving Neoadjuvant Chemotherapy for Breast Cancer.

ABSTRACT

OBJECTIVE: We aim to delineate the relationship between breast and axillary pathologic complete response (pCR) in patients receiving neoadjuvant chemotherapy for breast cancer. METHODS: We performed a retrospective cohort study of patients with clinical T1-4N0-3M0 breast cancer receiving neoadjuvant chemotherapy followed by surgical therapy at Sunnybrook Health Sciences Centre in Toronto, Canada between 2014 and 2019. Clinicopathologic data were abstracted from the electronic medical record. Women were stratified into receptor subtypes as follows hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-), HR+/HER2+, HR-/HER2+ and HR-/HER2- (triple negative) and compared with Fisher's exact test. Our primary outcome was to assess the positive predictive value of breast pCR for determining axillary pCR, and vice versa. RESULTS: There were 374 breast cancers, with 109 (29.1%) achieving breast pCR (ypT0/Tis). Amongst node-positive tumours achieving breast pCR, rates of associated axillary pCR (ypN0/0i+) were as follows HR+/HER2- (2/6, 33.3%), HR+/HER2+ (12/13, 92.3%), HR-/HER2+ (15/17, 88.2%) and triple negative (15/17, 88.2%) (P = 0.02). Conversely, amongst node-positive tumours achieving axillary pCR, rates of associated breast pCR were HR+/HER2- (2/10, 20.0%), HR+/HER2+ (12/23, 52.2%), HR-/HER2+ (15/24, 62.5%) and triple negative (15/26, 57.7%) (P = 0.1). CONCLUSIONS: Breast pCR is a strong predictor of axillary pCR in women with HER2-positive and triple-negative breast cancers. Conversely, axillary pCR is a modest predictor of breast pCR for these subtypes. There is a poor relationship between breast and axillary pCR in women with hormone receptor-positive disease. These data may inform future de-escalation of surgery in women with HER2-positive and triple-negative disease.