Science / Medicine : Calculating Breast Cancer Risk

Researchers rely on an equation that takes into account four factors from a woman’s medical history:

* Age when menstruation began.

* The number of negative breast biopsies she has had.

* Her age at the birth of her first live-born child.

* Family history of breast cancer.

Here are two cases of women, both 40 years old.

Abby began menstruating at age 12. She has had one breast biopsy--the extraction of a tiny bit of tissue for diagnostic examination--that proved benign. She is childless and neither her motheres nor her sisters have ever had breast cancer. Based on this medical history, researchers calculate that she has a 10.1% chance of developing breast cancer within the next 30 years, about the same risk the average American woman faces.

Barbara began menstruating before age 12 and has had one breast biopsy that also proved benign. She had her first child before age 20, which helps to reduce her risk of breast cancer, but both her mother and her sister have had the disease, which greatly increases her risk. This woman has a 39.8% chance of developing breast cancer within the next 30 years, or about four times higher than the general population.

“This is the kind of person that really has an unusual risk,” said Mitchell H. Gail, head of the epidemiological-methods section at the NCI and a co-author of the paper. “This is a person who requires intensive observation.”