One study showed that 10% of women who had this test got an ambiguous or unknown result. This is caused by certain mutations that scientists aren't certain affects the risk of cancer. The options for patients that obtain this result are much the same as those who receive a negative test result. The fact that a patient has undergone genetic testing in the first place indicates a cancer risk, and therefore regular exams and checkups are highly recommended, so that doctors may fully understand and watch out for the ambiguous mutations.

As more research is conducted and more people are tested for BRCA1 or BRCA2 changes, scientists will learn more about these changes and cancer risk.[1]
  1. ^ BRCA: Cancer Risks and Testing (http://www.cancer.gov/cancertopics/factsheet/Risk/BRCA)