CHICAGO - When she was diagnosed with breast cancer, Mary Jo, a 47-year-old mother of three, was hardly surprised. After all, breast cancer killed her mother and struck her sister.

But seven years later, Mary Jo, who asked that her last name not be used, has decided against being tested for a gene mutation that can trigger breast and ovarian cancer - even though the outcome could affect her teenage daughters' futures.

She is not alone in her decision. A study found less than half of the people with a family history of breast or ovarian cancer wanted to know whether they carried the mutated gene, called BRCA1.