Transporter associated protein expression in uveal melanoma.
BACKGROUND/AIM: Transporter associated protein (TAP) is important for presenting peptides to major histocompatibility complex (MHC) class I molecules. Defects in TAP lead to decreased MHC class I expression. The immunoexpression of human leucocyte antigen (HLA) class I molecules and the TAP1 subunit were studied in primary uveal melanomas and correlated with the cell types and extrascleral extension. METHODS: The HLA class I antigen and TAP1 subunit were analysed by immunoperoxidase staining with monoclonal antibodies on 45 primary uveal melanoma archival specimens. The tumours were divided into two groups-group A: tumours with no extrascleral extension; group B tumours with extrascleral extension/liver metastasis. Immunoanalysis was done by a semiquantitative method. RESULTS: HLA class I antigen and TAP1 were decreased in 35 of 35 tumours with no extrascleral extension and positive in six of 10 tumours with liver metastasis. Decreased immunoexpression of HLA class I antigen and TAP1 in uveal melanomas with no extrascleral extension was significant (p<0.001). HLA class I antigen and TAP1 were negative in spindle cell melanomas (p<0.001). CONCLUSIONS: HLA class I antigen and TAP1 expression were decreased in uveal melanomas with no extrascleral extension and in spindle cell melanomas. Decreased expression of TAP1 may lead to decreased expression of HLA class I antigen in uveal melanomas. This preliminary observation deserves further investigation, which may shed more light on the immune escape mechanisms of this tumour and thus enable novel therapeutic strategies.