"Most cancers are not hereditary," she says. "For example, only about 10% of breast cancers are inherited. The rest are "sporadic" -- that is, they occur because of a confluence of factors."
That's why Arun suggests that before deciding to be tested, you consult a genetic counselor.
Counselors help assess the chances that a person will develop a disease such as cancer. Often, the first step in the process is making a family tree, then looking for such "red flags" as having had many relatives who:
contracted cancer before age 50
contracted more than one primary cancer, or
had the same or a related cancer (for example, breast and ovarian).
She recommends that women who've been diagnosed with breast cancer and suspect it's hereditary get tested before beginning treatment.
"The results might indicate the risk of contralateral breast cancer (second new primary in the opposite breast) and help with surgical decision making, for example, considering bilateral mastectomy," she says.
"Also, new targeted drugs are in development that specifically target hereditary (BRCA-related) breast cancer, and patients might be eligible for these studies."