Abnormal expression of MHC class I molecules in malignant cells is a frequent occurrence that ranges from total loss of all class I antigens to partial loss of MHC specific haplotypes or alleles. Different mechanisms are described to be responsible for these alterations, requiring different therapeutic approaches. A complete characterization of these molecular defects is important for improvement of the strategies for the selection and follow-up of patients undergoing T-cell based cancer immunotherapy. Precise identification of the mechanism leading to MHC class I defects will help to develop...