What is your risk for breast cancer? New genetic test aims to provide answers


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Breast cancer is one of the most worrisome diagnoses a woman can get, and now women know that they can get a heads-up if they have an extra-high risk by getting a genetic test.

Mutations in dozens of different genes can raise the risk of breast cancer, but the two best-known risk genes are BRCA1 and BRCA2. Everyone carries these genes. When breast cancer, ovarian cancer or prostate cancer runs in a family, doctors often advise getting a test to assess whether a patient carries a risky version of one of them.


Now there are home tests for common BRCA1 and BRCA2 mutations. Some clearly raise a woman’s risk of cancer, and she can get more regular mammograms or, as actress Angelie Jolie opted to do, have her breasts surgically removed.

However, many people have mutations called variants of uncertain significance. It’s not known whether they raise cancer risk.

Mutations are mistakes in the genetic code, represented by the letters A, T, C and G repeated over and over again. Big mistakes in the code mean that the BRCA genes don’t work right and don’t fix the damage in cells that can lead to cancer.

But the BRCA1 gene is 10,000 letters long. A lot of little mistakes can turn up in a sequence that long, and not all of them mean cancer.


How can you tell which mutations lead to cancer?

Jay Shendure at the University of Washington and colleagues think they’ve come up with a way to tell. They painstakingly created mutations one by one in a batch of cancer cells that die when they carry mutations that affect a gene’s function.

To do this, they used a precision DNA editing method called CRISPR. They created nearly 4,000 single-letter mutations, one by one, in their dishes of cells and found that they could predict which mutations might raise the risk of cancer.

They won’t be able to say precisely how those mistakes would affect development of cancer in a living human being, but when they compared their findings with known cancer-causing mutations, they aligned.

The method might be used to help tell people with so-called variants of uncertain significance whether they should worry.