Second, there are no data, to our knowledge, on the efficacy of single-drug anti-PD-1 or anti-PD-L1 immunotherapy in patients with relapsed peritoneal mesothelioma; this is probably because of the very small number of patients with the disease, which would make a placebo-controlled randomised trial in this group very challenging. Here, CD274 is linked to peritoneal mesothelioma.