BACKGROUND: Pembrolizumab is the first-line standard of care for advanced non-small cell lung cancer (NSCLC) with a PD-L1 tumour proportion score (TPS) ≥ 50PS) 2 patients may receive pembrolizumab, despite the absence of sustaining evidence. PATIENTS AND METHODS: GOIRC-2018-01 is a multicentre, retrospective, observational study. PS 2 NSCLC patients with a PD-L1 TPS ≥50line pembrolizumab from June 2017 to December 2018 at 21 Italian institutions were included. Clinical-pathological characteristics were correlated with disease response and survival outcomes; adverse events were recorded. The primary objective was 6-months progression-free rate (6-months PFR). RESULTS: One hundred fifty-three patients (median age 70 years) were enrolled. At a median follow-up of 18.2 months, median progression-free survival (PFS) and overall survival (OS) were 2.4 (95 95 1.6-2.5) and 3.0 months (95.4-3.5), respectively. 6-months PFR was 27951-35. Patients with a PS 2 determined by comorbidities (n = 41) had significantly better outcomes compared with disease burden-induced PS 2 (n = 112). Indeed, 6-months PFR was 499 median PFS 5.6 versus 1.8 months and OS 11.8 versus 2.8 months, respectively. Additional potential prognostic factors (radiotherapy, antibiotics, steroids received before pembrolizumab) correlated with clinical outcomes. The determinant of PS 2 resulted the only factor independently impacting on both PFS and OS. No toxicity issues emerged. CONCLUSIONS: Outcomes of PS 2 NSCLC patients with PD-L1 TPS ≥50line pembrolizumab were globally dismal but strongly dependent on the reason conditioning the poor PS itself.