In situ expression of transforming growth factor beta is associated with melanoma progression and correlates with Ki67, HLA-DR and beta 3 integrin expression.

Transforming growth factor-beta (TGF beta), which is secreted by cultured melanoma cells constitutively, inhibits the proliferation of normal melanocytes and of most melanoma cells in vitro, but some melanoma cells from advanced stages of the disease develop resistance to TGF beta-dependent growth inhibition, without developing any change in TGF beta cell surface binding. In vitro TGF beta also downregulates the expression of HLA-DR molecules on melanoma cells, and upregulates the expression of the beta 3 integrin subunit on some cell lines. Immunohistochemical analysis of 53 melanocytic lesions (12 naevi, 30 primary melanomas and 11 metastases) revealed a trend of increasing expression of TGF beta and TGF beta receptor type III with tumour progression, and a significantly higher expression of both TGF beta (P < 0.0001) and the receptor (P < 0.05) in metastatic and thick (> 1 mm) primary melanomas compared with thin (< 1 mm) primary melanomas. The expression of TGF beta correlated with expression of a marker of proliferation, Ki67, and with HLA-DR and beta 3 integrin subunit expression. Coexpression of the four molecules was observed in all metastases and in most thick primary melanomas. These findings argue against an inhibitory effect of TGF beta on cell proliferation or HLA-DR antigen expression in melanoma, and suggest the upregulation of the beta 3 subunit. TGF beta protein appears to be a biological marker of melanoma progression in situ.