Pembrolizumab, an anti-PD-1 antibody, results in tumour response in around 15% of patients with advanced gastric cancer who have a PD-L1 combined positive score of at least 1. Lenvatinib, a multikinase inhibitor of VEGF receptors and other receptor tyrosine kinases, substantially decreased tumour-associated macrophages and increased infiltration of CD8 T cells, resulting in enhanced anti-tumour activity of PD-1 inhibitors in an in-vivo model. We aimed to assess the combination of lenvatinib plus pembrolizumab in patients with advanced gastric cancer in a phase 2 study.This study was an open-label, single-arm, phase 2 trial undertaken at the National Cancer Center Hospital East (Chiba, Japan). Eligible patients were aged 20 years or older and had metastatic or recurrent adenocarcinoma of the stomach or gastro-oesophageal junction, an Eastern Cooperative Oncology Group performance status of 0 or 1, and measurable disease according to the Response Evaluation Criteria in Solid Tumors (RECIST version 1.1), irrespective of the number of previous lines of treatment. Patients received 20 mg oral lenvatinib daily plus 200 mg intravenous pembrolizumab every 3 weeks until disease progression, development of intolerable toxicity, or withdrawal of consent. The primary endpoint was objective response rate according to RECIST, analysed in all patients who were eligible and received protocol treatment at least once. The safety analysis included all those who received protocol treatment at least once, regardless of eligibility. This study is registered at ClinicalTrials.gov, NCT03609359, and enrolment is complete.Between Oct 15, 2018, and March 25, 2019, 29 patients were enrolled in the first-line or second-line settings. At data cutoff (March 20, 2020), the median follow-up was 12·6 months (IQR 10·5-14·3). 20 (69%, 95% CI 49-85) of 29 patients had an objective response. The most common grade 3 treatment-related adverse events were hypertension (in 11 [38%] patients), proteinuria (five [17%]), and platelet count decrease (two [7%]). No grade 4 treatment-related adverse events, serious treatment-related adverse events, or treatment-related deaths occurred.Lenvatinib plus pembrolizumab showed promising anti-tumour activity with an acceptable safety profile in patients with advanced gastric cancer. On the basis of these results, a confirmatory trial will be planned in the future.Merck Sharp & Dohme.