This invention provides a method for reversing the cancerous phenotype of a cancer cell by introducing a nucleic acid having the melanoma differentiation associated gene (mda-7) into the cell under conditions that permit the expression of the gene so as to thereby reverse the cancerous phenotype of the cell. This invention also provides a method for reversing the cancerous phenotype of a cancer cell by introducing the gene product of the above-described gene into the cancerous cell so as to thereby reverse the cancerous phenotype of the cell. This invention also provides a pharmaceutical composition having the melanoma differentiation associated gene (mda-7) or the gene product of the melanoma differentiation associated gene (mda-7) effective to reverse the cancerous phenotype of a cancer cell and a pharmaceutically acceptable carrier.