Your mother hasn’t had breast cancer. Neither have her sisters or her mother. So there’s no need to worry about a family risk of breast cancer, right?

Wrong.

Telling your doctor whether relatives from your father’s side of the family have had breast cancer is just as important in determining a woman’s risk for developing the disease. But a new study shows that women often leave this information out when discussing their medical history with physicians.

Researchers say some women may not realize their father’s side of the family plays an equal role in risk for breast cancer. Some women also may not be reporting the information because they don’t know their fathers or because families may not pass breast cancer history on to their sons.

Researchers from Virginia Commonwealth University studied nearly nine-hundred women over forty. About sixteen percent of the women reported breast cancer in their mother’s families. But only ten percent reported that their paternal relatives have had the disease.

Statistics show that about five to ten percent of breast cancers are genetic. Up to eighty percent of women with a mutation of a certain gene develop breast cancer. Family history is the best way doctors have in initially assessing a woman’s risk for these forms of the disease.

Doctors say the findings are important for women and men. Men should know their family history to pass to their daughters. And women must remember not to leave out the other side of their family’s medical story.