There is no denying that breast cancer poses a significant threat to women, but new research shows that the threat is not nearly as great as most women perceive it to be.

The numbers are frightening. The American Cancer Society estimates that about 211,000 women will be diagnosed with invasive breast cancer in 2005 and just over 40,000 will die of the disease.

When asked to estimate the average lifetime chance of developing breast cancer, nine out of 10 women overestimated the risk. In a new study, the average woman guessed that the risk was three times higher than it actually was.

The study was conducted by researchers from the University of Michigan Health System and was published in the June issue of the journal Patient Education and Counseling.

"Breast cancer is so commonly in the news, and most of us can think of friends or relatives who have been diagnosed with it. That leads us to overestimate how common it really is," says study researcher Peter Ubel, MD, who directs the University of Michigan Center for Behavioral and Decision Sciences in Medicine.

"We forget that we know a lot of people with breast cancer because we know a lot of people."

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Estimating Risk

Roughly one in eight women will eventually develop breast cancer. In other words, a woman has a 13 percent chance of developing breast cancer at some point during her life.

When Ubel and colleagues asked 178 women to estimate the average woman's lifetime breast cancer risk, 89 percent overestimated. On average they thought a woman's chance of getting breast cancer was close to 50 percent.

The women were then counseled about their actual breast cancer risk. Researchers asked the women how anxious or relieved the medical counseling made them, and whether they thought a 13 percent lifetime risk was high or low.

"After estimating that 46 percent of women will be diagnosed with breast cancer, when they find out it's actually 13 percent, that seems relatively low and women feel a sense of relief," says Angela Fagerlin, PhD, who led the research team.

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Numbers Don't Give Context

Ubel tells WebMD that the findings have implications both for researchers and for doctors charged with educating patients about breast cancer risk. He says that asking them to estimate their own risk can help put the actual risk in perspective.

"We shouldn't just throw numbers at patients without giving them some context for those numbers," he says. "If you tell a patient that her breast cancer risk is [13 percent], that still may sound like a high risk to her. But if they guess a much higher number, as most do, [13 percent] is reassuring."

The University of Michigan study is not the first to show that women tend to overestimate their breast cancer risk. In a survey conducted by the American Cancer Society in 2001, nearly half of the women questioned believed that their risk was between 30 percent and 50 percent.

Many also wrongly believed women in their 30s and 40s are more likely to be diagnosed with breast cancer than older women.

Only about 18 percent of breast cancer diagnoses occur in women in their 40s, while about 77 percent of women with breast cancer are older than 50 when they are diagnosed, according to ACS figures.

Researcher Lisa M. Schwartz, MD, says cancer awareness campaigns often scare people with numbers that highlight the magnitude of cancer risk but provide little context.

Schwartz and colleagues with Dartmouth Medical School's VA Outcomes Group created a series of cancer risk-assessment charts to help people understand their true risk of dying from the disease.

While it is true that 40,000 women die from breast cancer each year, the risk of dying in your 40s and even 50s remains quite small, she notes. A 40-year-old woman who has never smoked, for example, has a 0.2 percent chance of dying from breast cancer before she is 50, and her risk will be less than 1 percent until she reaches age 70.

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By Salynn Boyles, reviewed by Michael W. Smith, MD

SOURCES: Fagerlin, A. Patient Education and Counseling, June 2005; vol 57: pp 294-299. Peter A. Ubel, MD, associate professor of internal medicine; director, program for improving health care decisions, University of Michigan, Ann Arbor. Lisa M. Schwartz, MD, associate professor of medicine, Dartmouth Medical School; senior researcher and co-director, VA Outcomes Group. WebMD Medical News: "How Likely Are You to Get Breast Cancer?" American Cancer Society's Cancer Reference Guide.