Tremelimumab combined with durvalumab in patients with mesothelioma (NIBIT-MESO-1): an open-label, non-randomised, phase 2 study

Background: Tremelimumab, an anti-CTLA4 monoclonal antibody, initially showed good activity when used alone in patients with mesothelioma, but did not improve the overall survival of patients who failed on first-line or second-line chemotherapy compared with placebo in the DETERMINE study. We aimed to investigate the efficacy and safety of first-line or second-line tremelimumab combined with durvalumab, an anti-PD-L1 monoclonal antibody, in patients with malignant mesothelioma. Methods: In this open-label, non-randomised, phase 2 trial, patients with unresectable pleural or peritoneal mesothelioma received intravenous tremelimumab (1 mg/kg bodyweight) and durvalumab (20 mg/kg bodyweight) every 4 weeks for four doses, followed by maintenance intravenous durvalumab at the same dose and schedule for nine doses. The primary endpoint was the proportion of patients with an immune-related objective response according to the immune-related modified Response Evaluation Criteria in Solid Tumors (RECIST; for pleural mesothelioma) or immune-related RECIST version 1.1 (for peritoneal mesothelioma). The primary analysis was done by intention to treat, whereas the safety analysis included patients who received at least one dose of study drug. This trial is registered with the European Clinical Trials Database, number 2015-001995-23, and ClinicalTrials.gov, number NCT02588131, and is ongoing but no longer recruiting patients. Findings: From Oct 30, 2015, to Oct 12, 2016, 40 patients with mesothelioma were enrolled and received at least one dose each of tremelimumab and durvalumab. Patients were followed-up for a median of 19·2 months (IQR 13·8-20·5). 11 (28%) of 40 patients had an immune-related objective response (all partial responses; confirmed in ten patients), with a median response duration of 16·1 months (IQR 11·5-20·5). 26 (65%) patients had immune-related disease control and 25 (63%) had disease control. Median immune-related progression-free survival was 8·0 months (95% CI 6·7-9·3), median progression-free survival was 5·7 months (1·7-9·7), and median overall survival was 16·6 months (13·1-20·1). Baseline tumour PD-L1 expression did not correlate with the proportion of patients who had an immune-related objective response or immune-related disease control, with immune-related progression-free survival, or with overall survival. 30 (75%) patients experienced treatment-related adverse events of any grade, of whom seven (18%) had grade 3-4 treatment-related adverse events. Treatment-related toxicity was generally manageable and reversible with protocol guidelines. Interpretation: The combination of tremelimumab and durvalumab appeared active, with a good safety profile in patients with mesothelioma, warranting further exploration.