Introduction

Peripheral blood inflammatory indices are potential biomarkers in immuno-oncology. However, their prognostic value in programmed death-ligand 1 (PD-L1)-positive metastatic triple-negative breast cancer (mTNBC) treated with first-line pembrolizumab-based chemoimmunotherapy is uncertain. We evaluated associations with progression-free survival (PFS) and immunotherapy-related adverse events (irAEs).

Material and methods

In this retrospective multicentre study, 89 women with PD-L1-positive (combined positive score ≥ 10) mTNBC treated in 13 Polish centres (September 2022 to February 2025) received pembrolizumab 200 mg q3w plus chemotherapy. Baseline and pre-cycle 2 blood counts were used to calculate systemic immune-inflammation index, systemic inflammation response index (SIRI), neutrophil-to- lymphocyte ratio, platelet-to-lymphocyte ratio and lymphocyte-to-monocyte ratio. Progression-free survival was assessed using multivariate Cox regression models without predefined cut-offs. Associations with irAEs were evaluated using non-parametric tests.

Results

In multivariable analyses, none of the baseline inflammatory indices were significantly associated with PFS (9.3 months [95% CI: 6.6–14.7]). Early on-treatment changes (baseline to pre-cycle 2) were also not significantly associated with PFS, although ΔSIRI showed a non-significant trend (p = 0.08). No significant associations were found between inflammatory indices (baseline or dynamic) and irAEs.

Conclusions

In this real-world cohort of PD-L1-positive mTNBC treated first-line with pembrolizumab plus chemotherapy, baseline and early-change inflammatory indices were not independently associated with PFS or irAEs and do not support routine clinical use in this setting.