DEBORAH AMOS, host:
There seems to be one statistic about breast cancer that's always cited and that is, one in nine women will develop the disease over their lifetime. Though accurate, the statement can be misleading.
NPR's Allison Aubrey reports there's a way to get a good estimate of your individual risk.
ALLISON AUBREY: Forty-year-old Deb Feinberg, a healthy stay-at-home mom, was curious to know what her personal risk of developing breast cancer might be. And she agreed to let us look over her shoulder as she has logged on to the National Cancer Institute's risk calculator.
Ms. DEB FEINBERG (40-year-old Mom): Yeah, this is - it's a little anxiety-producing to be looking at this - looks like there are about seven questions and...
AUBREY: The first four questions ask about age: your current age, the age of your first menstrual period, and your age at the time your first child was born. Each of these factors can influence a woman's risk of developing breast cancer.
The fifth question asks how many first-degree relatives - meaning your mother, sisters or daughters - have had the disease.
Ms. FEINBERG: We don't have any breast cancer in our family that I'm aware of. So I'm going to say zero.
AUBREY: The last question asks about race or ethnicity. Feinberg chooses white and then hits the return key.
Ms. FEINBERG: Okay, calculate risk, here we go.
AUBREY: One second later, results appear on the screen.
Ms. FEINBERG: My five-year risk is 0.8 percent, and the average woman is 0.6 percent.
AUBREY: Now, there is some reassuring about these two numbers. The analysis printed down below says the same calculation also means that Feinberg's risk of not getting breast cancer over the next five years is 99.2 percent. Even with this interpretation, Feinberg's still a little concerned.
Ms. FEINBERG: It disturbs me, I guess, that I'm 0.2 percent higher than the average woman. I wonder if that has to do with how old I was when my first child was born.
AUBREY: She was 39, and that does affect this risk assessment. But the National Cancer Institute's Risk Calculator is by no means a perfect tool. It's based on what scientists learned from a large mammogram screening trial back in the 1970s that involved more than a quarter-million women.
After figuring out what the dominant risk factors were among the women in that study who developed breast cancer, scientists designed a prediction model, now called the Gail model, which is the engine behind the online calculator.
Mr. LAWRENCE WICKERHAM (Co-Chairman, National Surgical Adjuvant Breast and Bowel Project): Some people are surprised that their risks are as high. Many are actually pleasantly surprised that their risks are not as great as they had imagined.
Lawrence Wickerham co-chairs the breast cancer research group NSABP, which is funded by the National Cancer Institute. He says the Gail model provides a reliable estimate for the vast majority of women age 35 and older. The exception is the roughly 2 percent of women who carry genes linked to breast cancer.
When Deb Feinberg used the risk calculator, she was surprised there were no questions about her lifestyle, weight, or drinking alcohol - all of which she's heard may be linked to the disease. But Wickerham says they are not as important as age, family history, family and reproductive history and race.
Mr. WICKERHAM: The critical ones that Dr. Gail has identified are the dominant ones that determine lifetime risk.
AUBREY: Having just a handful of factors in the model means there's fewer chances for errors. Karla Kerlikowske, a professor of medicine at the University of California San Francisco...
Professor KARLA KERLIKOWSKE (Medicine, University of California San Francisco): When you do these models, you want something that's relatively simple and easy to measure.
AUBREY: And lifestyle isn't. No one can remember precisely what they eat or drink. But there are ways Kerlikowske would like to revive the Gail model. She would toss out the question asking women how old they were when their first baby was born. Not because other factors such as breast-feeding confound it, but because research suggests it is not as important as breast density.
Prof. KERLIKOWSKE: We've appreciated the significance of breast density for probably 30 years.
AUBREY: The trouble is, there's never been an automated way to measure in a mammogram, the volume of epithelial cells and surrounding tissue that are typically involved in breast cancer.
Prof. KERLIKOWSKE: We think if we had a quantitative measure of breast density that might add to the specificity of the model and really improve prediction for the individual woman.
AUBREY: For now, the current model, despite its imperfections, can help women put their personal risk in perspective. That's how Deb Feinberg sees it.
Ms. FEINBERG: I think it's valuable because it brings it to front of mind. These numbers just remind me that I can't afford not to be vigilant.
AUBREY: About annual exams and mammograms: that, Feinberg says, is the advantage of knowing.
Allison Aubrey, NPR News, Washington.
AMOS: You can find a link to the National Cancer Institute's breast cancer risk calculator at npr.org.
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