Pembrolizumab is a major treatment for recurrent or advanced non-small-cell lung cancer (NSCLC). However, data on its use and pharmacokinetics (PK) in older patients are limited. This open-label, multicenter, observational study evaluated real-world data on the safety, efficacy, and PK of pembrolizumab in older patients with NSCLC. In 99 patients aged ≥75 years, PK was determined by liquid chromatography-mass spectrometry on pretreatment samples. Performance status (PS), geriatric assessment (GA), overall response rate (ORR), progression-free survival (PFS), and overall survival (OS) were evaluated. The median age was 78 (75-87) years. PS was 2-3 in 14 patients. The median ORR, PFS, and OS were 47.5%, 8.0, and 20.5 months, respectively. Although PK and ORR were not significantly associated, patients with the lowest Cycle 1-trough quartile (Q1) experienced poorer PFS (Q1 vs. Q2-4; 3.4 vs. 11.8 months, P = 0.006) and OS (Q1 vs. Q2-4; 9.9 vs. 21.7 months, P = 0.005) than in other quartiles overall, and even in the PD-L1 ≥50% subset (PFS, Q1 vs. Q2-4; 4.1 vs. 14.7 months, P = 0.005; OS, Q1 vs. Q2-4; 9.4 vs. 22.1 months, P = 0.010). The Q1 subgroup was characterized by poor PS and lower albumin, and more frequent "weight loss ≥ 10%" on the GA. Pembrolizumab therapy had similar PK and efficaciousness in older as well as younger patients. In patients with PS ≥2, low albumin, and vulnerable GA, early increases in PK levels are less likely, potentially diminishing efficacy even when PD-L1 ≥50%.
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