HLA-G and melanoma: Not surprisingly, HLA-G expression, which has been observed in melanoma, glioma, breast, lung and ovarian cancer, is associated with poor patient survival [60–67] and plasma levels of soluble HLA-G, secreted by tumour cells as a result of alternative splicing, have been shown to correlate with the presence of circulating tumour cells and disease progression (figure 1f) [68].