MDA-7 (melanoma differentiation associated protein-7), also designated IL-24, was initially identified in cultured human melanoma cells following treatment with interferon-b and mezerin, a treatment that causes the cells to lose proliferative capacity and terminally differentiate. MDA-7 was shown to have antiproliferative properties in human melanoma cells and to reduce cell growth in tumors of diverse origin. The level of MDA-7 expression is inversely correlated with human melanoma progression, with the highest levels found in normal, proliferating melanocytes and the lowest levels found in metastatic melanoma. Overexpression of MDA-7 in human breast cancer cells has been shown to induce apoptosis and upregulate Bax expression in a p53-independent manner. However, MDA-7 does not elicit growth inhibition and apoptosis in normal, non-tumor cells.