Genetic testing is a powerful tool for fighting cancer. But even the most accurate test has one limitation… it can’t find what it doesn’t seek.

A recent breast cancer study published in the Journal of the American Medical Association shows how significant that limitation can be.

The study looked at two genes, BRCA-one [BRAKA-ONE] and BRCA-two [BRAKA-TWO]. Mutations in these genes can raise the lifetime risk of breast cancer to eighty percent, and increase the odds of ovarian cancer, too.

Researchers performed exhaustive screenings on the BRCA genes of three-hundred women with a family history of breast or ovarian cancer. Conventional genetic tests had already been done, with negative results.

Those initial tests identify specific, common BRCA mutations, and leave plenty of genetic ground unexplored.

The more extensive screenings revealed previously undetected mutations in twelve percent of the women. Twenty-two different mutations were found, fourteen of them new to science.

None of the mutations were common, but that’s small comfort to the women who had them. And doctors have already identified more than one-thousand potential cancer-causing mutations that strike each of the BRCA genes.

So what should women from high-risk families do if their conventional tests come back negative?

As more breast cancer susceptibility genes are found, comprehensive testing may become increasingly important. But so far, one of the two extensive screening methods used in this study isn’t yet available domestically. For now, doctors say regular screenings, including routine mammograms, should remain the foundation of follow-up care.