The major cause of mortality in patients with malignant melanoma is metastatic dissemination of primary tumors. Currently, there are no highly specific cellular markers for evaluating the metastatic potential of primary melanoma tumors. The long-term goals of this project are to discover diagnostic markers for the early detection of metastatic disease in patients with melanoma and to evaluate these markers as prognostic indicators for the clinical course of disease. To identify these molecules we proposed to use a phage display library of human single-chain variable fragment (scFv) antibodies. The library contains >108 different scFv antibody specificities, which they expect is sufficiently diverse to contain scFv antibodies recognizing metastasis-associated antigens. They will utilize a panning procedure to select a subset of scFv antibodies that bind to a line of cultured human melanoma tumor cells, which are highly metastatic in nude mice. From this subset they will remove scFv antibodies that can bind to an autologous subline of weakly metastatic human melanoma tumor cells. The scFv that remain will be screened for reactivity against tissue samples of primary tumor and metastatic lesions obtained from melanoma patients. They expect to discover scFv antibodies that specifically recognize metastasis-associated antigens in human melanoma lesions. These scFv antibodies will be used for the development of early diagnostic markers and prognostic indicators of metastatic dissemination of human melanoma.