Abstract: The present disclosure relates to conjugates, preferably, antibody-drug conjugates, directed against select non-transmembrane tumor antigens that are normally intracellular but can be secreted from cancer cells, such as human cathepsin D, and can be targeted in a way that enables the selective delivery of the conjugate to cancer cells. The design and mechanism of action disclosed enable the preferential delivery of the conjugate prodrug to cancer cells over normal cells for the purpose of selectively killing cancer cells. The uses of such conjugates for the treatment of cancer are described.