Baseline inflammatory indexes and prognosis for progression-free survival in first-line pembrolizumab plus chemotherapy for PD-L1-positive advanced triple-negative breast cancer: A Polish multicenter cohort study.

e13108 Background: Advanced cancer is a systemic disease with inflammation recognized as one of its key hallmarks. Ratios such as Systemic Immune-Inflammation Index (SII), Systemic Inflammation Response Index (SIRI), Neutrophil-to-Lymphocyte Ratio (NLR), Platelet-to-Lymphocyte Ratio (PLR) and Lymphocyte-to-Monocyte Ratio (LMR) reflect systemic inflammatory status and are considered valuable prognostic biomarkers in patients treated with immune checkpoint inhibitors. However, data regarding their relevance in PD-L1-positive metastatic triple-negative breast cancer (mTNBC) receiving first-line pembrolizumab plus chemotherapy remain scarce. In this study, we evaluated whether baseline inflammatory indexes predict progression-free survival (PFS) in a multicenter Polish cohort treated with chemoimmunotherapy. Methods: This retrospective study included 89 women who initiated chemotherapy and pembrolizumab from September 2022 to February 2025 in 13 oncology centers in Poland. Complete blood count was assessed before treatment initiation. Systemic inflammation indexes were calculated as SII = (platelet count × neutrophil count) / lymphocyte count, SIRI = (neutrophil count × monocyte count) / lymphocyte count, NLR = neutrophil count / lymphocyte count, PLR = platelet count / lymphocyte count, LMR = lymphocyte count / monocyte count. Median PFS was estimated and associations between baseline inflammatory indexes and PFS were assessed using multivariate Cox regression models (α = 0.05). Results: The median follow-up was 10.1 months (IQR 5.5–14.8) and mPFS was 9.3 months (95% CI: 6.6–14.7). OS data were immature (n = 15 deaths). Due to multicollinearity (VIF > 10), SII was excluded from the final multivariable Cox model. The proportional hazards assumption was met for all variables, and diagnostic plots confirmed the absence of influential observations and preserved model linearity. The final multivariable model included SIRI, NLR, PLR, and LMR. None of the inflammatory indices demonstrated a statistically significant association with PFS. Hazard ratios (HRs) with 95% confidence intervals (CI) were as follows: SIRI HR 1.14 (95% CI 0.84–1.53; p = 0.41), NLR HR 1.04 (95% CI 0.84–1.30; p = 0.72), PLR HR 1.00 (95% CI 0.99–1.00; p = 0.42) and LMR HR 0.85 (95% CI 0.63–1.14; p = 0.27). Global model tests were not statistically significant (likelihood ratio p = 0.20; Wald p = 0.20; score p = 0.20). The concordance index was 0.59, indicating limited discriminative performance. Conclusions: In this real-world cohort, inflammatory indexes did not serve as prognostic factors for PFS in patients with PDL1-postive mTNBC treated with chemoimmunotherapy. These findings highlight the need for alternative biomarkers to optimize treatment.