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STUDIES FIND MORE EVIDENCE OF GENE-CANCER LINK

Scientists in Utah, at the National Institutes of Health and at the Johns Hopkins Medical Institutions have uncovered more evidence that defects in the p16 gene may be the cause of cancer.

Three papers on separate research projects published in the September issue of Nature Genetics, Washington, D.C., underline the importance of the defects in p16. The gene was identified in April by Myriad Genetics Inc., based in Research Park on the University of Utah campus.Myriad announced that the gene seemed to be a multiple tumor suppressor and implicated in a large range of cancers, including those of the lung, breast, brain, bone, skin, bladder, ovary and blood. But after the announcement other scientists said the range might not be that large.

According to an article by Carlos Caldas and others at Johns Hopkins in Baltimore, pancreatic cancers have an association with defects in the p16 gene.

In the same issue of Nature Genetics, Myriad Genetics reported on two families with melanoma, skin cancer, whose members have mutated p16 genes.

The third paper in the journal reported that a group of scientists from the National Institutes of Health, based in Bethesda, Md., found eight alterations of the p16 gene in DNA from melanoma patients with a history of the disease.

Dr. Stephan A. Hahn of the pathology department of Johns Hopkins, one of the authors of the article about pancreatic cancer, told the Deseret News that p16 has a high likelihood of being a tumor suppressor gene.

"We are pretty sure that p16 is atumor suppressor gene for pancreas (cancer), but we don't have functional proof for that," he said.

The way to prove it would be to replace a defective p16 gene in the test tube and see whether the culture develops tumors, he said.

What about the claim by Myriad that p16 is involved in a huge number of cancers? "That's at least a matter of debate," Hahn said. "I would say nobody really knows right now how many tumors finally are going to be driven by that tumor suppressor gene."

At least for now, the evidence seems to show that it doesn't include as many kinds of cancers as initially believed.

After the announcement in April, scientists around the world began looking for evidence that p16 is implicated in many cancers. They "didn't find the expected spectrum of mutations," he said.

Researchers are studying nearby regions of the p16 gene, which is found on chromosome 9p, to see if there are other tumor suppressor genes.

"People are checking the flanking areas (of the chromosome) for other genes, candidate genes" where defects may allow cancer to occur.

The p16 gene is not connected to another known tumor suppressor called p53, located on chromosome 17.

"P53 is so far the tumor suppressor gene," Hahn said.