Background and ImportanceCancer patients with comorbidities are usually excluded from clinical trials. Real-life observational studies are of particular interest to elucidate the safety of these new therapies.Safety of pembrolizumab +/- chemotherapy in metastatic non-small-cell lung carcinoma (NSCLC) was assessed in KEYNOTE-024, 189 and 407 pivotal trials.Aim and ObjectivesTo assess the safety of pembrolizumab +/- platinum-based chemotherapy in first-line treatment of metastatic NSCLC in real-world practice.Material and MethodsObservational, retrospective, single-centre study including 130 adult patients with stage IV NSCLC treated in first-line from 1 December 2017 to 31 December 2022, without EGFR or ALK mutations, autoimmune diseases or brain metastases, and performance status 0–1.Patients with PD-L1 ≥ 50% received pembrolizumab 200 mg or 2 mg/kg IV every 3 weeks. Those with non-squamous histology and PD-L1 < 50% received pembrolizumab + cisplatin IV 75 mg/m2 or carboplatin IV 6 AUC plus pemetrexed IV 500 mg/m2 every 3 weeks for 4 cycles plus maintenance with pembrolizumab + pemetrexed. Squamous cells and PD-L1 < 50% received pembrolizumab + IV carboplatin 6 AUC and IV paclitaxel 200 mg/m2 every 3 weeks for 4 cycles plus maintenance with pembrolizumab. Treatments were prolonged until progression or toxicity for a maximum of 2 years.A database was created to record adverse events (AEs) obtained from electronic medical records and according to Common Terminology Criteria for Adverse Events (CTCAE) Version 5.0.ResultsIn total, 491 AE of any grade and 78 of grade 3–4 were recorded. 10 patients discontinued treatment due to toxicity. AEs with incidence > 15% were (any grade – grade 3–4): anaemia (36–11), anorexia (51–2), asthenia (96–10), nausea (43–3), diarrhoea (25 -2), constipation (20–0), mucositis (21–2), neurotoxicity (22–1). Immune-mediated AEs were (any grade – grade 3–4): hepatotoxicity (7–3), nephritis (3–1), myocarditis (1–1), duodenojejunitis (1–1), pneumonitis (1–0).Conclusion and RelevanceMost patients suffered more than one AE. Even so, no deaths were related to toxicity (there were no grade 5 AEs). The six grade 3–4 immune-mediated AEs should be highlighted.References and/or AcknowledgementsConflict of InterestNo conflict of interest.