The Gail model calculates probabilities that a woman will develop invasive breast cancer during the next five years, and by age 90. "The assumption has always been that this model works well in women with atypia, but this had never been validated," says Shane Pankratz, 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 five 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.
Researchers tested the Gail model in 331 women with atypia who had benign breast biopsies 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.
Using these and other data, researchers also calculated the model's performance for individuals using the concordance statistic (c-statistic), which reflects how closely the actual timing of breast cancer events aligned with model predictions. A c-statistic of 0.5 is observed if the predictions are no better than random chance; a c-statistic of 1.0 is observed if the predictions are perfectly concordant with the actual outcomes. In this study, the c-statistic was 0.5, reflecting that the Gail model worked “no better than a coin flip”, so the researchers, in predicting which of the women with atypia would develop invasive breast cancer.
When assessed across other groups of women without respect to the presence of atypia, the Gail model typically performs better. In that setting, it has been shown to predict approximately the same number of breast cancers that later occur.
MEDICA.de; Source: Mayo Clinic