PDCD1 and melanoma: Data emerging from anti-PD-1 clinical trials indicate that checkpoint inhibitors are more beneficial for patients with lung metastasis than liver metastasis, for example.146–149 In melanoma patients, liver metastases have a lower density of CD8+ T cells at the tumour margin when compared with metastases in other organs,149 which could explain the reduced response to PD-1 inhibition at this site.