Abstract PS3-09-22: Er expression and age as key determinants of pathologic complete response (pcr) following neoadjuvant chemotherapy in patients with hormone receptor-positive, her2-negative early breast cancer. real world data

Abstract Background: Neoadjuvant chemotherapy remains a cornerstone in the treatment of patients with early-stage breast cancer and improves survival outcomes. Achievement of pathological complete response (pCR) have always been considered as a surrogate marker for better survival in patients with breast cancer and has been used as a primary endpoint in multiple clinical trials. However, patients with hormone receptor-positive (HR+) and human epidermal growth factor receptor 2 (HER2)-negative disease typically achieve low rates of pCR. Better understanding of the potential clinical and pathological variables affecting pCR in such population is important. Methods: This was a retrospective cohort analysis we conducted using electronic clinical and pathological data from patients diagnosed with early-stage breast cancer at one institution. All eligible patients included in the analysis had early HR+/HER2-negative disease: stage I, II, or III as per the American Joint Committee on Cancer (AJCC) 8th edition. Estrogen receptor (ER) expression by immunohistochemistry was stratified as: High (ER > 50%), intermediate (11-50%), low (1-10%) and negative (0%). Multivariable logistic regression was performed to identify independent predictors of pCR. We used multivariable logistic regression analysis to identify independent clinical and/or pathological predictors for pCR. Results: Out of 2724 patients included in the analysis; 1039 patients were treated with neoadjuvant chemotherapy. Median age was 50 (22-83) years. Most (n= 864, 83.1%) patients had invasive ductal carcinoma (IDC), while (n= 92, 8.8%) patients had invasive lobular carcinoma (ILC). Majority (n=870, 83.7%) patients had high ER-expression; 44 patients (4.2%) intermediate ER-expression, 59 patients (5.6%) low ER-expression, while 63 patients (6%) had ER-negative (but PR-positive) disease. 758 (72.9%) had clinical node-positive disease. The overall pCR rate in this population was 10.9% (n=114). Younger age was significantly associated with higher pCR rates: 15.0% in patients