Major pathologic response and long-term clinical benefit in hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer after neoadjuvant chemotherapy.

e12608 Background: Rates of pathological complete response (pCR) are much lower in patients with hormone receptor–positive (HR+) /HER2-negative (HER2-) breast cancer than in those with HER2-positive and triple-negative breast cancer (TNBC). The majority of HR+/HER2- breast cancer patients can also achieve long-term survival despite not attaining pCR, indicating limited prognostic value of pCR in this population. This study aimed to identify novel pathologic end points for predicting long-term outcomes in HR+/HER2- breast cancer after neoadjuvant chemotherapy. Methods: We analyzed HR+/HER2- breast cancer patients with stage II-III tumors who underwent curative surgery after neoadjuvant chemotherapy from three hospitals. Major pathologic response (MPR), defined as the presence of Miller-Payne grades 3-5 and positive lymph node ratio of ≤10%, was used as a pathological evaluation indicator. MPR evaluates the extent of residual invasive carcinoma in both the breast and axillary lymph nodes following neoadjuvant therapy. We assessed the association between MPR and event-free survival (EFS) and performed Multivariable Cox regression to identify independent factors associated with EFS. Results: From January 2010 to December 2020, 386 patients were included in the final analysis. The median age was 46 years. 244 patients (63.2%) were premenopausal, with 271 (70.2%) patients diagnosed with stage III disease. The predominant neoadjuvant chemotherapy regimen was anthracycline combined taxane (79.3%). 28 patients (7.3%) achieved pCR and 118 patients (30.6%) achieved MPR. The median duration of follow-up was 54.4 months. Multivariate analysis showed that PR expression, Clinical stage, Miller–Payne grades and Positive lymph node ratio were independent prognostic factors for EFS (all P values <0.05). The prognostic effect of MPR remained in multivariable models (hazard ratio (HR), 0.45; 95% confidence interval (CI), 0.26–0.76; P = 0.008), with 5-year EFS of 87% vs. 68% in the non-MPR group. In non-pCR patients, those who achieved MPR exhibited a similar EFS compared with pCR patients (HR, 2.25; 95% CI, 0.51–9.84; P = 0.28). Conclusions: MPR was a novel pathologic end point for prognostic evaluation in HR+/HER2- breast cancer after neoadjuvant chemotherapy. Compared to pCR, MPR may hold greater applicability in the prognosis evaluation.