A statistical model commonly used to predict the risk of breast cancer in women was not accurate when used to evaluate women with atypical hyperplasia, according to a new Mayo Clinic study published in the Oct. 14, 2008, issue of the Journal of Clinical Oncology.
Atypical hyperplasia (atypia) describes breast tissue with an increased growth of abnormal cells that might become cancerous.
The Gail model calculates probabilities that a woman will develop invasive breast cancer during the next five years, and by age 90. The model has come to be called by the name of its developer, National Cancer Institute researcher Mitchell Gail, M.D., Ph.D. Its original purpose was to identify groups of high-risk women for participation in breast cancer chemoprevention studies. But the model has since been used in clinical settings to counsel individuals about their risk of developing breast cancer. Predicting risk at an individual level is much more challenging than when risks can be averaged across groups.
"The assumption has always been that this model works well in women with atypia, but this had never been validated," says Shane Pankratz, Ph.D., Mayo Clinic statistician and a lead investigator in the study. "We found that, for the group of women with atypia, the model predicted significantly fewer invasive breast cancers than were actually observed, and we also observed that the model was not able to reliably identify the women who were actually at higher risk of developing breast cancer."
The Gail model considers the woman's family history of breast cancer, her age, and her ages at the onset of menstruation and at first live birth, as well as the number of breast biopsies undergone and presence of atypical hyperplasia found in biopsies. About 5 percent of women who undergo biopsies for suspicious lumps or other breast concerns have atypia. About 25 percent of those with atypia will develop cancer within 25 years.
Mayo Clinic researchers tested the Gail model in 331 women with atypia who had benign breast biopsies at Mayo Clinic between 1967 and 1991. Of these women, 58 developed cancer during an average of 13.7 years of follow-up. In contrast, the model predicted that 34.9 women would develop breast cancer in that period.