Tremelimumab for patients with chemotherapy-resistant advanced malignant mesothelioma: an open-label, single-arm, phase 2 trial

Background Monoclonal antibodies to cytotoxic T-lymphocyte antigen 4 (CTLA4) have therapeutic activity in differenttumour types. We aimed to investigate the efficacy, safety, and immunological activity of the anti-CTLA4 monoclonal antibody, tremelimumab, in advanced malignant mesothelioma. Methods In our open-label, single-arm, phase 2 study, we enrolled patients aged 18 years or older with measurable, unresectable malignant mesothelioma and progressive disease after a first-line platinum-based regimen. Eligible patients had to have a life expectancy of 3 months or more, an Eastern Cooperative Oncology Group performance status of 2 or less, and no history of autoimmune disease. Patients received tremelimumab 15 mg/kg intravenously once every 90 days until progressive disease or severe toxicity. The primary endpoint was the proportion of patients who achieved an objective response (complete or partial response), with a target response rate of 17% according to the modified Response Evaluation Criteria in Solid Tumors (RECIST) for pleural malignant mesothelioma or standard RECIST 1.0 for peritoneal malignant mesothelioma. Analyses were done according to intention to treat. This trial is registered with EudraCT, number 2008-005171-95, and ClinicalTrials. gov, number NCT01649024. Findings Between May 27, 2009, and Jan 10, 2012, we enrolled 29 patients. All patients received at least one dose of tremelimumab (median two doses, range one to nine). No patients had a complete response and two patients (7%) had a durable partial response (one lasting 6 months and one lasting 18 months); one partial response occurred after initial progressive disease. Thus, the study did not reach its p rima ry endpoint. However, we noted disease control in nine (31%) patients and a median progression-free survival of 6 . 2 months (95% CI 1 . 3-11 . 1) and a median overall survival of 10 . 7 months (0 . 0-21 . 9). 27 patients (93%) had at least one grade 1-2 treatment-emergent adverse event (mainly cutaneous rash, pruritus, colitis, or diarrhoea), and four patients (14%) had at least one grade 3-4 treatmentemergent adverse event (two gastrointestinal, one neurological, two hepatic, and one pancreatic). Interpretation Although the effect size was small in our phase 2 trial, tremelimumab seemed to have encouraging clinical activity and an acceptable safety and tolerability profile in previously treated patients with advanced malignant mesothelioma.