Researchers trying to understand the origins of cancer have identified a key gene that may be tied to cancer of the colon.

According to a study published Friday in Science magazine, scientists in Maryland, Texas and Utah discovered that a gene called p53 is commonly found to be mutated, or even missing, in tumors of the colon.The scientists suspect their newly discovered gene is a so-called anti-oncogene, a gene that normally suppresses cancer. If so, it is one of several such genes identified. The first one found is involved in retinoblastoma, a tumor that most often arises in the eyes of very young children.

Mutation or loss of the retinoblastoma gene seems to remove the brakes, allowing the runaway process of cancer to begin. The retinoblastoma gene has also been implicated in other tumors, such as bone and breast cancers.

The discovery of such genes has become important diagnostically, allowing doctors to predict which infants are especially susceptible to retinoblastoma. Such predictions have already let doctors save the eyesight of a few children.

If a diagnostic test based on the p53 gene can be developed for cancer of the colon, doctors may be able to predict who is susceptible, and perhaps even detect the disease before symptoms arise.

In the study published this week, the researchers at Johns Hopkins University, the University of Utah and the Baylor College of Medicine report that in 53 of the 56 colon tumors they examined, a loss of genetic material was evident.

Scientists believe that cells normally have two good copies of each cancer-suppressor gene. In some cases people may inherit only one copy of a given suppressor gene, and so be predisposed to develop tumors. If and when the second copy of the gene fails, tumor growth begins.

Even in patients who inherit two good copies of the gene - and who thus have no predisposition to the tumor - cancer may arise if both copies of the p53 gene are damaged or lost.