HLA-G and melanoma: β2-microglobulin, which is encoded by B2M, is an essential component of MHC class I. Previous studies on pancreatic ductal adenocarcinoma, colorectal cancer, and melanoma showed that loss of B2M was an indicator of poor dismal prognosis, including lymph node metastasis, recurrence, and therapy resistance [11, 24, 25].