Studies on the biology of cell signaling have led to the discovery of a large number of extra-cellular peptide signaling molecules (1). These small molecules act on multiple targets in the human body at a distance in the circulation at very low concentrations (<10−8 M). They are tightly bound to their receptors (Ka≥ 108), and they control and modulate the function of almost all key organs and metabolic processes (2). In many cases the regulatory peptide action is mediated through specific membrane-bound receptors, often of the G-protein coupled type, with seven trans-membrane helical domains. This cell receptor specificity gives these peptides great potential usefulness in cancer diagnosis and therapy (3). Related potential targeting molecules include interleukins (4), integrin ligands (5), and regulatory molecules like fibroblast growth factor.