B2M and metastatic melanoma: Mutations in Janus kinase 1/2 (JAK1/2) and beta-2-microglobulin (B2M) were found in both primary and acquired resistance to anti-PD-1 antibody (pembrolizumab) or anti-CTLA-4 (ipilimumab) in metastatic melanoma patients [19,20,28].