all neoplastic cells express one or more members of a unique family of cell surface ubiquinone oxidase proteins with protein disulfide - thiol interchange activity that are characteristically inhibited by quinone site inhibitors with anti - cancer activity . cancers of different cellular or tissue origins express different tnox cancer isoforms or combinations of isoforms and shed these proteins into the circulation . herein are disclosed methods both for cancer detection and diagnosis of particular origin , based on the patterns and molecular weights of the isoforms which allow the identification of the cell type and or tissue of origin of the neoplasm . relative tnox amounts are proportional to tumor burden and provide a reliable measure of response to therapy and disease progression .