CTLA4 and mesothelioma: In the large negative randomized DETERMINE trial of tremelimumab [antibody against cytotoxic T-lymphocyte associated protein 4 (CTLA-4)] versus placebo [4], PeM was included, but only 18 patients with peritoneal disease were enrolled (out of 571 total mesothelioma patients), thereby preventing subgroup analysis for efficacy specifically in PeM.