Identifying determinants of pathologic complete response in patients with breast cancer after receiving neoadjuvant systemic therapy

e12622 Background: In locally advanced breast cancer, neoadjuvant systemic therapy aims to downstage the disease, clear micrometastasis, assess chemosensitivity, and allow for breast conserving surgery. The attainment of a Pathologic Complete Response (pCR) has been associated with improved event free survival (EFS) and improved overall survival (OS) among various studies. We aim to identify clinicopathological factors which may influence pCR. Methods: This is a single center retrospective study of patients diagnosed with locally advanced breast cancer from 2017-2022 who received neoadjuvant therapy and investigating predictors of pCR in this subset of patients. Descriptive statistics were used to summarize the baseline characteristic variables. Variables relating to pCR were analyzed by binary logistic regression and chi-square test. A p-value of < 0.05 was considered statistically significant. Results: Of the 165 patients included, all were female, with a mean age of 50 and majority (97%) with invasive ductal carcinoma (IDC) histology. Baseline characteristics are summarized. 52 had hormone (HR)pos/Her2neg, 51 with triple negative, 47 had HR pos/Her2pos, and 15 had HR neg/Her2pos disease. pCR was seen in 36% of patients. A normal BMI of < 25 (p=0.03), nonsmoker (p=0.01), grade III (p=0.01), HR pos/Her2pos (p=0.02), and HR neg/Her2pos (p=0.0001), were associated with pCR. In patients with triple negative breast cancer, the use of immunotherapy did not influence pCR (p = 0.0565). There were no differences based on age, race, menopausal status, stage, size, presence of LVI or DCIS or multifocal disease. In the 157 patients where Ki-67 was known, tumors with higher Ki-67 values of 30-49% and > 50% achieved pCR compared to those with lower Ki-67 (p = 0.002). Conclusions: Those with normal BMI, non-smokers, and aggressive clinicopathological factors such as Her2 positive, higher Ki67 (30% and above), and grade III disease were more likely to achieve pCR after neoadjuvant systemic therapy. These findings further identify tumor characteristics most likely to respond to neoadjuvant chemotherapy. [Table: see text]