New technologies, and a little help from the U.S. Supreme Court, have made it possible for large numbers of women to find out whether they carry genetic mutations that increase their risk of breast cancer - a development warmly welcomed by experts in the field.

But the availability and relative affordability of multigene-panel tests can also lead to anxiety and confusion about what course of action to choose, because the risk associated with many of those genes remains unknown.

"Genetic testing holds a lot of potential and a whole lot of uncertainty," said Beth Peshkin, a professor of oncology and senior genetic counselor at Georgetown Universitys Lombardi Comprehensive Cancer Center in Washington.

"The more genes we test, the more variants were likely to find," explained Peshkin. "A recent study found that about 40 percent of people who underwent panel testing had variants, or genetic changes, that we dont know how to interpret."

In 2013 the Supreme Court invalidated Myriad Genetics patents on the two major genes that predispose women to breast and ovarian cancer, ruling that human genes cannot be patented.

Since then, several companies have begun testing for mutations in those genes, BRCA1 and BRCA2, which are responsible for about 80 percent of hereditary breast cancer cases; and the genes have been incorporated into panels that use so-called next-generation sequencing to test for multiple genes simultaneously.

The problem arises because some of the mutations detected in those panels are relatively rare and scientists do not yet know how much additional risk they confer, if any.

In August, the New England Journal of Medicine published a study showing that certain mutations in a gene called PALB2 were associated with a lifetime risk of between 33 percent (for carriers with no family history of breast cancer) and 58 percent (for those with a strong family history). Thats similar to the risk associated with a BRCA2 mutation, but lower than that for BRCA1.

The average lifetime risk for an American woman is about 12 percent. The vast majority of breast cancer cases are not linked to any known hereditary factor.

"Investigators from 14 centers around the world pooled data from all of their families with PALB2 mutations," said Dr. Jane Churpek, co-director of the Comprehensive Cancer Risk and Prevention Program at University of Chicago Medicine. "So, for the first time, we had a large enough series to get an estimate (of risk) for carriers of mutations in this gene. The hope is well see similar efforts for each gene on these panels."

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Breast cancer genetic screening offers vital information, uncertainty