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New study finds big batch of cancer genes

A batch of new gene discoveries nearly doubles the number of genes known to cause three of the most common cancers – breast cancer, prostate cancer and ovarian cancer. While each gene alone affects only a small number of people, taken together they help explain one-third of cases of these cancers, researchers reported on Wednesday.

It took a giant study to find all the genes – nearly 200,000 people took part at 160 institutions. The findings can not only help doctors decide who needs more frequent screening for cancer, but may eventually help target treatments that will work better for particular patients, the researchers said.

People with several of the genetic changes linked with cancer will have a much higher-than-average risk of the cancers, the researchers said. They published their findings in a series of 13 papers in several medical journals, including Nature Genetics and Nature Communications.

“By looking for people who carry most of these variations we will be able to identify those who are at the greatest risk of getting these cancers and then targeting screening tests to these individuals,” said Douglas Easton of Britain’s University of Cambridge, who led some of the studies.

“We now have 76 common genetic variants which are associated with breast cancer risk,” Easton told a news conference. Combined with other research, including the well-known breast cancer genes BRCA1 and BRCA2, genetic susceptibility explains 40 percent of breast cancer cases, he said.

“Any one of those (variants) is so tiny they don’t affect much,” Dr. Fergus Couch of the Mayo Clinic in Rochester, Minn., who worked on the project, told NBC News. “But when we put them together into a complex model … It’s the power of everything together that can make a difference.”

The researchers found 23 new genes linked with prostate cancer and three more for ovarian cancer. Now researchers know about 78 different genes associated with higher prostate cancer risk, and 16 of them are associated with aggressive disease.

The three cancers affect 2.5 million people globally, killing about a third of them. They all are driven by hormones.

“The most immediate practical application is probably going to be for women already at high risk of (breast cancer),” Easton said. A woman with a BRCA1 or BRCA2 mutation already has a very high chance of breast cancer. If she also has one or more of these other alterations, she’s at even higher risk.

Women who have a BRCA1 mutation along with most of the other, newly discovered mutations have an 80 percent chance of developing breast cancer by age 80, the researchers found.

“The 1 percent of people who have lots of these alterations could see their risk of developing prostate cancer increase by nearly 50 percent and breast cancer by 30 percent,” Easton said.

People may soon be able to take a genetic test to see what their risk is. They could then opt for early screening to watch for the disease. “This will be ready for prime time in a little more than a year,” Couch predicted.

Right now, guidelines vary on when women should get mammograms, for instance. Some guidelines call for annual screening starting at age 50; others say women only need them every two years.

A woman with a high genetic risk might opt to start having mammograms at age 30 or younger. There’s also confusion around testing for prostate cancer. U.S. experts say men shouldn’t be routinely screened using a blood test called a PSA test, because it causes too many “false positives” – when men are initially told they may have cancer but it turns out they don’t.

But men with a high genetic risk might opt to have frequent PSA tests.

“These results are the single biggest leap forward in finding the genetic causes of prostate cancer yet made,” said Rosalind Eeles  of Britain’s Institute of Cancer Research.

“They allow us, for the first time, to identify men who have a very high risk of developing prostate cancer during their lifetime,” she added.

The genes play a variety of roles in cancer. Some are supposed to stop the out-of-control growth that marks a tumor; some help cancer cells spread.