Nearly 20 percent of women may overestimate or underestimate their breast cancer risk because of a misunderstanding of genetic and lifestyle factors that can lead to the disease, according to a new study by the University of Michigan Comprehensive Cancer Center.
 

The findings, published in the journal Patient Education and Counseling, are part of a larger study examining how to improve patients' understanding of risk information. The researchers surveyed nearly 700 women who were deemed at risk of developing breast cancer. They found 1 in 5 of the women didn't believe their actual risk numbers, saying they did not take into account their family history of cancer or their personal health habits.
 

"If people don't believe their risk numbers, it does not allow them to make informed medical decisions," said Angela Fagerlin, associate professor of internal medicine at the University of Michigan Medical School and a research scientist at the VA Ann Arbor Center for Clinical Management Research.
 

"Women who believe their risk is not high might skip chemoprevention strategies that could significantly reduce their risk. And women who think their risk should be higher could potentially undergo treatments that might not be medically appropriate, which can have long-term ramifications," she added.
 

For the study, 690 women at above-average risk of developing breast cancer completed a web-based survey that included questions about age, ethnicity, history of breast cancer, and number of first-degree relatives with the disease. They then were told their five-year risk of developing cancer and given information about prevention strategies.
 

The women were then asked to recall their risk of breast cancer within the next five years. The results showed that 22 percent of the women who misreported their risk said they disagreed with the numbers.
 

Many said their family history made them either more or less likely to develop breast cancer. One-third of women cited a gut instinct that their risk numbers just seemed too high or too low. Some mistakenly felt a lack of family history of cancer meant their own risk should be very low. Others believed that because an aunt or father had cancer, it increased their risk. But the investigators noted only first-degree female relatives — mother, sister, daughter — impact a person's breast cancer risk.
 

"We've put so much fear in people about breast cancer so they feel at high risk," said lead researcher Laura D. Scherer. "We found that many women assumed certain factors should impact their risk, like cancer history in distant or male relatives, but those factors don't put a woman at increased risk.
 

"We have a trend toward personalized medicine and individualized medicine, but if people don't believe their personalized risk numbers, they're not going to get the best medical care for them."
 

While heart disease is the leading killer of men and women, more than 234,000 Americans will be diagnosed with breast cancer this year and 40,000 will die from it, according to the American Cancer Society.