A new study has recently revealed that women with atypical hyperplasia are at higher risk of developing breast cancer in future than previously thought.

Mayo Clinic study found that hundreds of women with these benign lesions indicate that their absolute risk of developing breast cancer grows by over 1 percent a year. The study found that after five years, 7 percent of these women had developed the disease; after 10 years, that number had increased to 13 percent; and after 25 years, 30 percent had breast cancer.

The finding places the more than 100,000 women diagnosed each year with atypical hyperplasia, also known as atypia, into a high-risk category, where they are more likely to benefit from intense screening and use of medications to reduce risk.

Previous research has shown that women with atypia have a fourfold to fivefold increased "relative risk," meaning that they are four to five times more likely to develop breast cancer than women who don't have these lesions. But few studies have had the patient numbers and follow-up time to report the patients' "absolute risk," the chance that she will develop breast cancer over a certain period of time.

Importantly, the Mayo findings were validated by researchers at Vanderbilt University using biopsies from a separate cohort of women with atypia. Both data sets revealed that at 25 years following biopsy, 25 to 30 percent of these women had developed breast cancer.

The researchers were able to give an even more accurate estimate of risk by incorporating information from a patient's pathology specimen. They found that as the extent of atypia in a biopsy increased, as measured by the number of separate atypia lesions or foci, so did the woman's risk of developing breast cancer. For example, at 25 years post-biopsy, 47 percent women with three or more foci of atypia in the biopsy had developed breast cancer, compared to only 24 percent of women with one focus.

Based on these results, the research team recommends that women with atypical hyperplasia be recognized as having significantly increased lifetime risk of breast cancer and thus be candidates for screening MRI. Moreover, anti-estrogen medications like tamoxifen have already been tested in clinical trials in women with atypia and shown to lower their risk of breast cancer by 50 percent or more.

Yet, Dr. Degnim said many women with atypia are not taking the medications, in part because they and their physicians have not had solid estimates of their breast cancer risk to guide them.

The study is published in the Journal of Medicine.