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Scientists find possible third breast cancer gene

Scientists find possible third breast cancer gene

WASHINGTON (Reuters) -- Researchers said on Monday they may have identified a third gene involved in breast cancer and said it might be responsible for a significant number of hereditary breast cancers.

The researchers still have to identify the actual gene, and have to confirm it is found around the world, but think it explains many cases of hereditary breast cancer, the kind that runs in families.

"We've located what looks like a very good region in the human genome in which to search for a third breast cancer susceptibility gene," Dr. Olli Kallioniemi of the National Human Genome Research Institute (NHGRI) said in a statement.

"If these results are confirmed, this new gene could account for up to one third of the hereditary breast cancer cases that cannot be explained by BRCA1 or BRCA2 in the Nordic population."

Kallioniemi and 34 other scientists in the United States, Finland, Sweden, Iceland and Germany worked on the study, which has tracked the responsible gene to the arm of chromosome 13.

Two genes already are strongly linked with hereditary breast cancer -- BRCA1 and BRCA2.

They can explain up to 50 percent of some hereditary cases. But Kallioniemi said these probably are what he calls "extreme cases." He said the families studied in the work that led to the discovery of BRCA1 and BRCA2 were unusual.

"They were the most extreme type of hereditary cases, where a single family could have five or six affected cases with very, very early onset," he said in a telephone interview.

"But that is not the predominant form of familial disease or familial cancer. The most common types are such that there are only a couple of breast cancer cases in the family, and not necessarily a dramatic early age of onset."

And most cases of breast cancer do not involve an inherited gene but instead what is called a sporadic mutation.

"The percentage of hereditary cases is 5 to 10 percent," Kallioniemi said. "The vast majority of breast cancer cases have no family history."

To try to explain the family-linked cases that did not involve BRCA1 and BRCA2, the international team first looked at 37 tumors from breast cancer patients who did not have the known mutations.

They identified the possible involvement of chromosome 13. Then they went to actual patients, studying 77 Finnish, Icelandic and Swedish families with breast cancer but who did not have mutations of BRCA1 and BRCA2.

It is easy to study cancer in these countries because they keep careful records of cancer cases.

"Out of the families that are not explained by BRCA1 or 2, possibly a third are explained by this cause," Kallioniemi said. He said he thinks the mutation is probably found in populations everywhere, not just the Nordic countries.

Now the researchers are trying to confirm that this is indeed the case, and also trying to home in on the gene itself. Kallioniemi said having the human genome sequence -- finished earlier this summer -- will help a great deal.

"We will have a template to compare the sequences that we got from cancer patients," he said.

Kallioniemi stressed that the research, while important, cannot yet help any cancer patient. "Families are very anxious to learn about additional clues that may help them or help them diagnose their susceptibility to cancer," he said.

Currently, women who believe they have a high risk of breast cancer can be tested to see if they have BRCA1 or BRCA2 mutations. They can then be more careful about getting mammograms, can take a drug, tamoxifen, that might help prevent cancer, or can have their breasts removed.

"If a new gene is found, it will provide another important means of diagnosis for families who are at risk of developing hereditary breast cancer," Dr. Heli Nevanlinna, of Helsinki University Central Hospital in Finland, said in a statement.

Copyright 2000 Reuters. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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