The formula--called the Breast Cancer Risk Assessment Model--estimates women's risk of breast cancer using information such as the age at which they had their first period, the age at which they had their first child, whether any close relatives have had breast cancer, and other variables.
Researchers developed the model using data from studies of white women, and some have long been concerned that it underestimated the risk for black women--particularly since recent studies have begun to suggest that breast cancer tends to be more deadly among black women than white women. More than 19,000 black women are diagnosed with breast cancer each year, and almost 6,000 die from it, according to the Washington Post.
"We've been concerned about the assumptions we had to make for African American women and other racial and ethnic groups for some time," Dr. Mitchell Gail told the newspaper. Gail both led the team that developed the original tool and led the recent reassessment.
For the original model, Gail and his team used data collected from more than 240,000 white women. For the new study, they used data from a recent study of more than 3,200 black women, half of whom had breast cancer.
To test the new model's accuracy, they used it to predict the cancer risk of more than 14,000 black women enrolled in a study called the Women's Health Initiative, which collected data to look at risk factors for many diseases and conditions in women. The new model predicted that 323 of the women would be diagnosed with breast cancer during the study. In reality, 350 were--which, Gail told the Chicago Tribune, "is pretty close."
The accuracy of the old model for black women depends on many factors, the researchers found. It particularly underestimated risk for older black women, and occasionally overestimated risk for young women. But overall, it underestimated risk for black women in 90 percent of all scenarios, the researchers found.
For example, the old model found that the five-year risk for a 50-year-old black woman, who began menstruating at age 11, had her first child at 27, and had a mother or sister with breast cancer was 1.22 percent. The new model found that her risk would be 1.84 percent.
"That doesn't seem like a big difference, but even though those numbers look small, they can effect decisions," Gail told the Washington Post.
For example, Gail and his colleagues examined the records of 20,000 black women who had applied to take part in a breast-cancer prevention trial of the drugs tamoxifen and raloxifene. To participate, women needed to have a risk factor of at least 1.66 percent. Using the old model, only 14.5 percent of the women qualified; with the new model, 30.3 percent would have.
The new risk model could also influence the recommendations doctors make to black women regarding preventative measures such as mammograms and taking preventative drugs.
"This is extremely significant," Lovell A. Jones, director of the Center for Research and Minority Health at the University of Texas, told the Washington Post. "This is emblematic of a broader problem, which is: We tend to make the assumption that one size fits all. One size does not fit all."
Gail and his colleagues plan to make a version of the new model available to the public on the National Cancer Institute's Web site this spring.