Until now, researchers had only a hunch that colon cancer is inherited. Though the disease runs in families, it is so common (striking 152,000 people in the United States every year) that several cases in one family could be merely coincidence or the result of a common diet or environment. But the research team, led by Vogelstein and by Albert de la Chapelle of the University of Helsinki, found that cancer patients in two large families have an identical, mutant stretch of DNA on chromosome 2 which healthy relatives do not. Though not the cancer gene itself, this mutant may be caused by that gene, and serve as a marker, or warning sign, that the gene is present.
The discovery has also revealed what may be an entirely novel way that genes cause cancer. Biologists have known for years that many tumors arise when one of about 10 genes that suppresses cancer is turned off, by a mutation or carcinogen, or when one of 100 known cancer-causing “oncogenes” makes a normal cell malignant. But colon tumor cells are riddled with aberrant DNA, report researchers led by Dr. Stephen Thibodeau of the Mayo Clinic, as if the genes were churned out by a malfunctioning Xerox machine. The cancer gene may prevent DNA from making faithful copies of itself when cells divide. As a result, cells have hundreds of thousands of mutations, which may explain why the colon-cancer gene is also linked to cancers of the uterus, stomach and other organs.
Until scientists find the gene itself, they won’t be sure how it causes cancer, let alone how to prevent it. But once a blood test can identify carriers, they can get regular colonoscopies, which detect incipient malignancies. With that, says Vogelstein, 90 percent can be spared death from colon cancer.
