Abstract PO5-17-01: Pre-treatment tumor infiltrating lymphocytes are associated with higher likelihood of pathologic complete response among black women with TNBC receiving neoadjuvant chemoimmunotherapy

Abstract Background: High risk, early-stage triple negative breast cancer (TNBC) is a heterogenous disease that is associated with early recurrence and high mortality, particularly among black women as compared to their white counterparts. Pathologic complete response (pCR) to neoadjuvant chemotherapy (NACT) is a strong-predictor of long-term disease-free survival in TNBC, and the KEYNOTE-522 trial demonstrated that the addition of immunotherapy (pembrolizumab) to NACT resulted in a higher likelihood of pathologic complete response (pCR) in high-risk early-stage TNBC. Following these findings, the standard of care has been to administer the K522 regimen (K522R) in the neoadjuvant setting for patients with high risk early-stage TNBC. However, our understanding of the clinical and tumor characteristics to prognosticate response to K522 are lacking, and additional real-world data is needed to better understand if these variables differ among race. Methods: We evaluated 76 patients who were treated with the K522R at our institution. There were slides available from 29 patients’ pre-treatment biopsies for pathology review. In the available slides, tumor infiltrating lymphocytes (TIL) were evaluated as the percentage of lymphocytes in the stroma within the tumor area. For the remaining cases that did not have available slides, these variables were retrieved from pathology reports and patients’ charts. Patient characteristics including age, race and body mass index (BMI) were acquired via retrospective chart review. These clinicopathologic variables were correlated with pCR, which was defined by the absence of invasive carcinoma in the breast and axillary lymph nodes at the time of surgery. Binary logistic regression analysis was performed to correlate the above variables with pCR versus residual disease (RD). Results: Seventy-six pre-treatment biopsy specimens treated with the K522R were evaluated. The patient population spanned a broad spectrum of age, body habitus, and race, with mean age 55, mean BMI 28.3, and predominantly black (over 60 percent) population. At the time of analysis, 64 of the 76 patients had completed the K522R and subsequently undergone surgery at our institution. Of the 64 patients who had undergone definitive surgery, 31 (48.4%) achieved pCR. In univariate analysis, pre-treatment TIL was significantly associated with attainment of pCR, with TIL of 28.5% (± 19.1) in patients who achieved pCR versus 9.73% (± 9.40) in those who had RD (95% CI 1.03-1.21, p=0.014*). When TIL was further stratified by race, mean percentage of TIL was significantly higher among black women who achieved pCR (27.5% ± 4.7) compared to black women with RD (12.2% ± 3.05) (95% CI 0.021 – 0.197, p=0.016*). Additionally, mean percentage of TIL was higher overall among black women when compared to the white patients in our cohort, though this finding was not statistically significant (p=0.252). Conclusion: Our real-world data demonstrates high levels of pre-treatment TIL are significantly associated with achievement of pCR in patients with TNBC treated with the K522 regimen. When TIL was further stratified by race, black patients were found to have higher TIL than white patients. Within the black population, a statistically significant difference in TIL percentage was found in those achieving pCR compared to those with RD. It is well understood that black women often have poorer breast cancer outcomes than white women, and our finding of higher TIL percentage among this population, along with the significant association between TIL and attainment of pCR with chemoimmunotherapy, could have important implications for optimization of therapy. Further exploration of this phenomenon in larger, diverse breast cancer populations is warranted. Citation Format: Sarah Wood, Ji-Hoon Lee, Yuan Gao, Xiaoxian Li, Jane Meisel. Pre-treatment tumor infiltrating lymphocytes are associated with higher likelihood of pathologic complete response among black women with TNBC receiving neoadjuvant chemoimmunotherapy abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-17-01.