B2M and neoplasm: To date, loss or down-regulation of the HLA-I molecules in tumour cells has been reported in a variety of human malignancies as one of the main mechanisms of cancer cells to escape from the anti-tumour T cell immunity.6–8 Alteration of HLA gene transcription, translation or post-transcriptional modification, as well as mutation of the B2M gene, might cause HLA-I down-regulation.9,10