Genes may predict cancer risk

Malcolm Ritter / The Associated Press /

Published Mar 29, 2013 at 05:00AM

The hope for patients is that doctors may one day have genetic tests that help them determine which women would benefit more from mammograms and which men would be helped by tests for prostate cancer. The payoff, farther in the future, could also be new treatments.

NEW YORK — A huge international effort involving more than 100 institutions and genetic tests on 200,000 people has uncovered dozens of signposts in DNA that can help reveal further a person’s risk for breast, ovarian or prostate cancer, scientists reported Wednesday.

It’s the latest mega-collaboration to learn more about the intricate mechanisms that lead to cancer. And while the headway seems significant in many ways, the potential payoff for ordinary people is mostly this: Someday there may be genetic tests that help identify women with the most to gain from mammograms, and men who could benefit most from PSA tests and prostate biopsies.

And perhaps farther in the future these genetic clues might lead to new treatments.

“This adds another piece to the puzzle,” said Harpal Kumar, chief executive of Cancer Research U.K., the charity which funded much of the research.

One analysis suggests that among men whose family history gives them roughly a 20 percent lifetime risk for prostate cancer, such genetic markers could identify those whose real risk is 60 percent.

The markers also could make a difference for women with BRCA gene mutations, which puts them at high risk for breast cancer. Researchers may be able to separate those whose lifetime risk exceeds 80 percent from women whose risk is about 20 to 50 percent. One doctor said that might mean some women would choose to monitor for cancer rather than taking the drastic step of having healthy breasts removed.

Scientists have found risk markers for the three diseases before, but the new trove doubles the known list, said one author, Douglas Easton of Cambridge University. The discoveries also reveal clues about the biological underpinnings of these cancers, which may pay off someday in better therapies, he said.

Experts not connected with the work said it was encouraging but that more research is needed to see how useful it would be for guiding patient care.

Easton said the prospects for a genetic test are greater for prostate and breast cancer than ovarian cancer.

Breast cancer is the most common malignancy among women worldwide, with more than 1 million new cases a year. Prostate cancer is the second most common cancer in men after lung cancer, with about 900,000 new cases every year. Ovarian cancer accounts for about 4 percent of all cancers diagnosed in women, causing about 225,000 cases worldwide.

The new results were released in 13 reports in Nature Genetics, PLOS Genetics and other journals. They come from a collaboration involving more than 130 institutions in the United States, Europe, and elsewhere. The research was mainly paid for by Cancer Research U.K., the European Union and the U.S. National Institutes of Health.

Scientists used scans of DNA from more than 200,000 people to seek the markers, tiny variations in the 3 billion “letters” of the DNA code that are associated with disease risk.

The scientists found 49 new risk markers for breast cancer plus a couple of others that modify breast cancer risk from rare mutated genes, 26 for prostate cancer and eight for ovarian cancer. Individually, each marker has only a slight impact on risk estimation, too small to be useful on its own, Easton said. They would be combined and added to previously known markers to help reveal a person’s risk, he said.

A genetic test could be useful in identifying people who should get mammography or PSA testing, said Hilary Burton, director of the PHG Foundation, a genomics think-tank in Cambridge, England. A mathematical analysis done by her group found that under certain assumptions, a gene test using all known markers could reduce the number of mammograms and PSA tests by around 20 percent, with only a small cost in cancer cases missed.

For patients like Vicki Gilbert of England, who carries a variation of the BRCA1 gene, having details about her cancer risk would have made decision-making easier.

Gilbert, 50, found out about her genetic risk after being diagnosed with the disease in 2009. Though doctors said the gene wouldn’t change the kind of chemotherapy she got, they suggested removing her ovaries to avoid ovarian cancer, which is also made more likely by a mutated BRCA1.

“They didn’t want to express a definite opinion on whether I should have my ovaries removed so I had to weigh up my options for myself,” said Gilbert, a veterinary receptionist in Wiltshire. “... I decided to have my ovaries removed because that takes away the fear it could happen. It certainly would have been nice to have more information to know that was the right choice.”

Gilbert said knowing more about the genetic risks of cancer should be reassuring. “There are so many decisions made for you when you go through cancer treatment that being able to decide something yourself is very important,” she said.

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