264P Tumor-infiltrating Lymphocytes (tils) for Prediction of Response to Platinum-Based Neoadjuvant Chemotherapy (NACT) in Triple-Negative Breast Cancer (TNBC): Final Analysis

According to several previous trials, event-free survival (EFS) in patients with TNBC is improved when carboplatin is added to NACT. Stromal TILs represent an important predictive and prognostic biomarker in patients with breast cancer. We are now reporting the analysis of EFS in patients with TNBC who received NACT ± carboplatin regarding TILs status. The clinical data were obtained from 132 patients diagnosed with TNBC (ER&PgR<10%) and treated with either anthracycline-taxane NACT (n=68) or carboplatin-based chemotherapy (n=64) from 2017 to 2022 at N.N. Petrov National Medicine Research Center of Oncology. TILs were evaluated in FFPE tumor tissue samples stained with H&E at baseline biopsies according to guidelines from the International TILs Working Group. EFS was estimated by the Kaplan-Meier method and compared between groups by log-rank test. Multivariate analysis for EFS was performed using Cox's proportional hazards regression model, covariates included TILs level (<40 vs. ≥40), NACT, nodal status, BRCA status and pCR. High TILs were associated with significantly higher 5-year EFS (94.3% vs 56.1% HR=0.119, 95%CI 0.02-0.88, р=0.037). Patients with pCR had a significantly better 5-year EFS (74.5% vs 53.2%, HR=0.231, 95%CI 0.09-0.58, р=0.002). 5-year EFS rates were similar for both platinum-based and standard NACT groups (68.6% and 61.9%, respectively HR=0.537, 95%CI 0.24-1.19, p=0.124). 5-year EFS for platinum-based NACT was 100% vs 84.6% in the standard NACT group (HR=1.374, 95%CI 0.66-2.88, р=0.40) in patients with high TILs, compared with patients with low TILs levels EFS was lower 61.3% vs. 56.9%, respectively (HR=1.602, 95%CI 0.71-3.61, р=0.256). In univariate analysis, the nodal status, pCR, and TILs level were significant predictors of EFS. In multivariate analysis, only pCR (p=0.006) and TILs level (p=0.048) are two independent predictors of EFS. EFS is numerically lower in the low TILs tumors which justifies the escalation of the NACT regimen. Treatment de-escalation may be considered in patients with high TILs level. Further research in larger datasets is needed to validate these hypothesis generating findings.