Comparison of First-Line Pembrolizumab Monotherapy Versus Chemo-Immunotherapy in Metastatic Non-Small Cell Lung Cancer Patients with PD-L1 TPS ≥ 50%: A Multicenter Real-World Study from Turkey

Background and Objectives: This study aimed to compare the real-world outcomes of first-line pembrolizumab monotherapy (Mono-IO) versus pembrolizumab plus platinum-based chemotherapy (IO + ChT) in patients with metastatic non-small cell lung cancer (mNSCLC) and a PD-L1 tumor proportion score (TPS) ≥ 50%. Materials and Methods: This retrospective, multicenter, real-world study evaluated 148 patients with mNSCLC and PD-L1 expression ≥ 50% who received either first-line Mono-IO or IO + ChT. Overall survival (OS), progression-free survival (PFS), and clinical benefit rate were compared between the two treatment strategies. Additionally, clinical prognostic factors, patterns of progression, and post-progression treatments were analyzed. Survival outcomes were assessed using Kaplan–Meier estimates, multivariable Cox regression, and restricted mean survival time (RMST) analysis. Results: Patients in the Mono-IO group were significantly older (median 69 vs. 63 years; p < 0.001) and had a higher proportion of ECOG PS 2 (35.3% vs. 5.2%; p < 0.001). No significant differences were observed between Mono-IO and IO + ChT in median OS (32.0 vs. 26.0 months; p = 0.559) or PFS (19.6 vs. 19.4 months; p = 0.572). In an exploratory multivariable analysis adjusting for organ-specific metastases and antibiotic exposure, ECOG PS ≥ 1 (aHR: 1.86, 95% CI: 1.16–2.97; p = 0.009), antibiotic use (aHR: 1.85, 95% CI: 1.16–2.95; p = 0.010), and liver metastasis (aHR: 2.58, 95% CI: 1.16–5.74; p = 0.020) were independent predictors of worse OS. Conversely, PD-L1 TPS ≥ 90% (aHR: 0.56, 95% CI: 0.35–0.91; p = 0.018) was independently associated with superior OS. In exploratory subgroup analysis, a numerical survival trend favoring Mono-IO was observed in patients with PD-L1 TPS ≥ 90%, although this finding remains hypothesis-generating. Following disease progression, 64.7% of patients received no further systemic therapy. Conclusions: In this real-world cohort, no statistically significant differences in OS or PFS were detected between Mono-IO and IO + ChT; however, the wide confidence intervals do not exclude clinically meaningful differences, and equivalence cannot be inferred from these data. PD-L1 TPS ≥ 90% may potentially serve as a biomarker to identify patients who derive benefit from monotherapy, although this exploratory finding requires validation in larger cohorts. Given that the majority of patients did not transition to subsequent therapy in routine practice, likely reflecting multifactorial host frailty and rapid disease evolution, first-line therapeutic optimization warrants careful individualized consideration.