Cancer gene test can be 100% accurate, scientists say

Scientists who developed test for colon cancer find way to improve it

February 17, 2000|By Jonathan Bor | Jonathan Bor,SUN STAFF

Johns Hopkins researchers who devised the first test for hereditary colon cancer say they have developed a technique that will raise the test's accuracy to 100 percent.

The technology should also improve testing for other diseases that run in families, including hereditary breast cancer, kidney cancer and cystic fibrosis, doctors say.

A report on the findings appears in today's issue of the journal Nature.

Dr. Bert Vogelstein, a researcher at the Johns Hopkins Oncology Center, said the finding was born of frustration after his laboratory's discovery in 1995 of the major genes responsible for hereditary colon cancer.

At the time, Vogelstein believed he had a test that could tell people with extensive family histories of colon cancer whether they carried the defective gene.

Scientists soon learned, however, that the test was capable of finding the mutation in only about half the people who carried it.

This stemmed from the fact that people carry two copies of each gene. In a particular test, a normal gene inherited from one parent could mask a defective gene inherited from the other.

To solve this problem, the Hopkins lab found a way to separate the two genes and analyze each one separately.

Together, two types of hereditary colon cancer account for about 5 percent of all cases of colon cancer -- or about 6,500 new cases in the United States each year. About the same percentage of breast cancer cases are hereditary.

"Even though all cancers are tragic, the hereditary cancers are of particular concern to us because these families have multiple members affected," Vogelstein said.

"The cancers occur at a very early age -- patients in their forties, thirties, even teens."

Screening tests are not useful for the general population, just for families that have a documented history of the disease.

"This technology does not change who is eligible to receive a genetic test, but it will make the tests much more useful for those who decide to take them," said Dr. Hai Yan, a research fellow in Vogelstein's lab.

People who learn they have a genetic predisposition can be monitored for early signs of the disease and possibly catch it earlier.

"Obviously, in these families it's a huge thing to find out who carries the gene," said Dr. Marston Linehan, a kidney cancer researcher at the National Cancer Institute. "Reading these tests can be a very complicated.

"With this, all of a sudden it's like taking your glasses off when they're foggy."

The conversion technology could add $250 to the cost of tests that already range from $1,000 to $10,000 depending on the disease.

In some cases, Vogelstein said, conversion could greatly lower the overall cost by simplifying the amount of work that must be done.

Hopkins owns the conversion technology, which it licenses to GMP Cos. of Fort Lauderdale, Fla.

The university will earn royalties from the any commercial applications.

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