The antitumour activity of PD-1 inhibitors has been reported in several types of squamous cell cancers. In a multicentre, randomized, open-label, phase III trial, patients with previously treated, unresectable advanced or recurrent oesophageal squamous cell carcinoma were randomly assigned to receive nivolumab (a PD-1 inhibitor) or investigator’s choice of chemotherapy. Nivolumab was associated with a significant improvement in overall survival (P = 0.019) and a favourable safety profile compared with chemotherapy and might represent a new standard second-line treatment option for these patients.