Like antibodies, peptides are molecules composed of amino acids covalently linked to each other. These are short protein segments, which may have a broad spectrum of biological action, including antitumor activity. In general, a bioactive peptide may specifically recognize a cell target, such as a receptor present on the plasma membrane, and thus activate a biochemical pathway, culminating in cell death by apoptosis or necrosis. Alternatively, certain peptides may be internalized in the cells and exert a cytotoxic effect through interaction with other cytosolic components. A peptide may furthermore promote an indirect antitumor effect by inhibiting angiogenesis or by activating the immune response against tumor cells.

Peptides may be chemically synthesized and modified in order to improve their stability and activity in vivo. The synthesis of peptides on an industrial scale and with clinical quality degree also makes its therapeutic use possible. For these reasons, bioactive peptides make up an important new class of drugs, which has attracted interest from the pharmaceutical industry. Currently, about 50 peptides are used worldwide for the treatment of different diseases.