A cDNA molecule corresponding to a newly discovered human gene is disclosed. The new gene, which is frequently deleted in liver cancer cells and cell lines, is called the DLC-1 gene. Because the gene is frequently deleted in liver cancer cells, but present in normal cells, it is thought to act as a tumor suppressor. This gene is also frequently deleted in breast and colon cancers, and its expression is decreased or undetectable in many prostate and colon cancers. Also disclosed is the amino acid sequence of the protein encoded by the DLC-1 gene. Methods of using these biological materials in the diagnosis and treatment of hepatocellular cancer, breast cancer, colon cancer, prostate cancer, and adenocarcinomas are presented.