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SUMMARY It has been recently established that there is a correlation between the lack of MHC class I gene expression on murine tumour cells and their ability to grow and metastasize. We have studied the expression of HLA‐ABC and HLA‐DR products on human malignant tumours from the digestive tract using monoclonal antibodies, by indirect immunofluorescence on the cell suspensions obtained from 29 freshly explanted digestive tumours. Our results show that digestive tract cancers have an heterogeneous expression of HLA class I molecules on their surface. Whereas 50% have high levels of expression of these molecules (more than 60% positive cells), 25% have a moderate level of expression (20‐60% positive cells) and 25% have weak expression (less than 20% positive cells). It has been found that there is a correlation between the level of HLA class I molecule expression and the degree of histological differentiation of a tumour. The absence of MHC class I antigens on human tumour cells, detected in this study, may play a relevant role in oncogenesis, as has been established in experimental models.

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