Pemetrexed and Platinum Plus Pembrolizumab in Patients With Metastatic Nonsquamous NSCLC by Tumor Burden at Baseline: A Post Hoc Efficacy Analysis of KEYNOTE-189

INTRODUCTION: The aim of this study was to evaluate the efficacy of pemetrexed and platinum plus pembrolizumab by baseline tumor burden. METHODS: A total of 616 patients in the intention-to-treat population of the KEYNOTE-189 study were included in this analysis. Baseline tumor burden subgroups were identified on the basis of extent of distant metastasis (M1a versus M1b), median number (≤3 versus >3) of organ systems with lesions, or symptom severity score of patient-reported lung cancer-associated symptoms (≤median versus >median). Overall survival (OS), progression-free survival (PFS), and PFS-2 were evaluated by Kaplan-Meier and univariate Cox methods. Objective response rate was analyzed using logistic regression models, and duration of response was analyzed descriptively. Efficacy outcomes were also analyzed according to the programmed death-ligand 1 expression levels. RESULTS: OS and PFS were significantly improved with pemetrexed and platinum plus pembrolizumab in all baseline tumor burden subgroups (M1a stage: OS hazard ratio [HR] = 0.54, p = 0.0037; PFS HR = 0.48, p = 0.0001; M1b stage: OS HR = 0.58, p ≤ 0.0001; PFS HR = 0.51, p ≤ 0.0001; number of organ systems with lesion ≤ 3: OS HR = 0.49, p ≤ 0.0001 PFS HR = 0.41, p ≤ 0.0001; >3: OS HR = 0.67, p = 0.0068; PFS HR = 0.59, p = 0.0001; symptom severity score ≤ median: HR = 0.51, p ≤ 0.0001; PFS HR 0.49, p ≤ 0.0001; > median: OS HR = 0.60, p = 0.0003; PFS HR = 0.48, p ≤ 0.0001). PFS2 and objective response rate were also improved with pemetrexed and platinum plus pembrolizumab in all baseline tumor burden subgroups. Efficacy outcomes were generally consistent regardless of programmed death-ligand 1 expression levels. CONCLUSIONS: Pemetrexed and platinum plus pembrolizumab were found to have relevant efficacy regardless of the extent of baseline tumor burden and the variables used to define it. These results further support pemetrexed and platinum plus pembrolizumab as the standard of care in the first-line treatment of metastatic nonsquamous NSCLC.