BACKGROUNDPenpulimab is a novel programmed death (PD)-1 inhibitor. This study aimed to establish the efficacy and safety of first line penpulimab plus chemotherapy for advanced squamous non-small-cell lung cancer.METHODSThis multicentre, randomised, double-blind, placebo-controlled, phase 3 clinical trial enrolled patients with locally advanced or metastatic squamous non-small-cell lung cancer from 74 hospitals in China. Eligible participants were aged 18-75 years, had histologically or cytologically confirmed locally advanced (stage IIIb or IIIc) or metastatic (stage IV) squamous non-small-cell lung cancer, were ineligible to complete surgical resection and concurrent or sequential chemoradiotherapy, had an Eastern Cooperative Oncology Group (ECOG) performance status of 0-1, did not have previous systemic chemotherapy for locally advanced or metastatic non-small-cell lung cancer, and had one or more measurable lesions according to RECIST (version 1.1). Participants were randomly assigned (1:1) to receive intravenous penpulimab 200 mg or placebo (excipient of penpulimab injection), plus paclitaxel 175 mg/m2 and carboplatin AUC of 5 intravenously on day 1 every 3 weeks for four cycles, followed by penpulimab or placebo as maintenance therapy. Stratification was done according to the PD-L1 tumour proportion score (<1% vs 1-49% vs ≥50%) and sex (male vs female). The participants, investigators, and other research staff were masked to group assignment. The primary outcome was progression-free survival assessed by the masked Independent Radiology Review Committee in the intention-to-treat population and patients with a PD-L1 tumour proportion score of 1% or more (PD-L1-positive subgroup). The primary analysis was based on the intention-to-treat analysis set (ie, all randomly assigned participants) and the PD-L1-positive subgroup. The safety analysis included all participants who received at least one dose of study drug after enrolment. This trial was registered with ClinicalTrials.gov (NCT03866993).FINDINGSBetween Dec 20, 2018, and Oct 10, 2020, 485 patients were screened, and 350 participants were randomly assigned (175 in the penpulimab group and 175 in the placebo group). Of 350 participants, 324 (93%) were male and 26 (7%) were female, and 347 (99%) were of Han ethnicity. In the final analysis (June 1, 2022; median follow-up, 24·7 months [IQR 0-41·4]), the penpulimab group showed an improved progression-free survival compared with the placebo group, both in the intention-to-treat population (median 7·6 months, 95% CI 6·8--9·6 vs 4·2 months, 95% CI 4·2-4·3; HR 0·43, 95% CI 0·33-0·56; p<0·0001) and in the PD-L1-positive subgroup (8·1 months, 5·7-9·7 vs 4·2 months, 4·1-4·3; HR 0·37, 0·27-0·52, p<0·0001). Grade 3 or worse treatment-emergent adverse events occurred in 120 (69%) 173 patients in the penpulimab group and 119 (68%) of 175 in the placebo group.INTERPRETATIONPenpulimab plus chemotherapy significantly improved progression-free survival in patients with advanced squamous non-small-cell lung cancer compared with chemotherapy alone. The treatment was safe and tolerable. Penpulimab combined with paclitaxel and carboplatin is a new option for first-line treatment in patients with this advanced disease.FUNDINGThe National Natural Science Foundation of China, Shanghai Municipal Health Commission, Chia Tai Tianqing Pharmaceutical, Akeso.