Baseline Systemic Inflammation Response Index and Clinical Outcomes in Heavily Pretreated Platinum-Resistant Ovarian Cancer Treated with Pembrolizumab Monotherapy.

Objective: Immune checkpoint inhibitor monotherapy has shown limited efficacy in platinum-resistant ovarian cancer (PROC), although a small subset of patients experiences durable disease control. We evaluated the association between baseline systemic inflammatory markers and the clinical outcomes of pembrolizumab monotherapy. Materials and Methods: We included 95 patients with PROC who received pembrolizumab monotherapy at Samsung Medical Center between 2018 and 2023. Durable disease control was defined as a progression-free survival (PFS) ≥ 6 months. The systemic inflammation response index (SIRI), neutrophil-to-lymphocyte ratio (NLR), and systemic immune-inflammation index (SII) were calculated from the pretreatment complete blood count. Associations with the PFS and overall survival (OS) were evaluated using multivariable Cox regression. Results: Among 94 patients evaluable for 6-month durable disease control, 10 (10.6%) achieved this endpoint. The patients with durable disease control had a lower baseline SIRI than those without durable disease control (median, 0.7 vs. 1.6; p = 0.019). In multivariable analyses, a higher log-transformed SIRI was associated with a shorter PFS (HR, 1.44; 95% CI, 1.13-1.83; p = 0.003) and OS (HR, 2.02; 95% CI, 1.53-2.67; p < 0.001). Conclusions: The baseline SIRI was associated with the PFS and OS in heavily pretreated patients with PROC receiving pembrolizumab monotherapy, and a lower SIRI was associated with durable disease control. The SIRI may provide readily available prognostic information in this setting; however, the data-derived cutoff requires prospective external validation and should not be interpreted as a predictor of the pembrolizumab-specific benefit.