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Summary: A new study gives women and their doctors a better idea of how much certain non-cancerous breast conditions may raise the risk of developing breast cancer later. Some raise the risk more than others, researchers report in the New England Journal of Medicine.

Why it's important: Wider use of mammograms has made it easier for doctors to spot benign breast disease, a known risk factor for breast cancer. About 10% of women who get a mammogram will end up needing a breast biopsy, and most of those biopsies will find benign breast disease rather than cancer. Women in this situation need a clearer picture of their breast cancer risk so they can take steps to lower it and possibly prevent the disease.

What's already known: Doctors have long known that women who develop certain non-cancerous breast conditions -- known as proliferative changes and atypical changes -- are more likely to develop breast cancer. But they weren't sure how much higher that risk was. This new study lays out the risk according to what type of benign breast disease a woman has, and whether she has a family history of breast cancer.

How this study was done: Researchers from the Mayo Clinic in Rochester, Minn., studied the medical records of more than 9,000 women who had been diagnosed with a non-cancerous breast condition at their clinic between 1967 and 1991. The women were asked about their family history of breast cancer and whether they themselves had developed breast cancer. The researchers used that information to calculate the risk associated with 3 types of non-cancerous breast conditions: non-proliferative lesions, proliferative lesions, and atypical (abnormal-looking) lesions. Non-proliferative changes usually involve cysts with no increased growth of normal breast cells. With proliferative changes, the cysts are accompanied by an overgrowth of normal-appearing cells, and when there is atypia, there is an overgrowth of cells that appear abnormal.

What was found: Two-thirds of the women had non-proliferative changes and most of the rest had proliferative changes without atypia. Only 4% had atypical changes. All 3 of these conditions raised breast cancer risk, but not by the same amount. Non-proliferative lesions raised the risk only slightly (27%); proliferative lesions nearly doubled a woman's risk; and atypical changes in the breast raised the risk more than fourfold. To help women understand the meaning of those increases, an editorial published along with the study translated those figures into real-world (absolute) terms -- specifying how many "extra" cases of breast cancer these changes would bring compared to women in the general population.

So if 5 out of 100 women in the general population were to get breast cancer, the study determined that 1 more woman, or about 6 out of 100 women with non-proliferative breast lesions, would get cancer. For women with proliferative changes, 5 more women would develop breast cancer, or about 10 out of 100. And for women with atypical changes, 14 more women, or about 19 out of 100 would be diagnosed with breast cancer.

Women who were younger than 45 when they developed benign breast disease had a higher risk of going on to develop breast cancer than did women who were 45 or older. And again, women with atypical lesions had the highest risk among the 3 types of disorders.

Women with atypical lesions had a higher risk of breast cancer regardless of their family history of the disease, but those with a strong family history had the highest risk. The same was true for women with proliferative lesions. The researchers defined "strong" family history as having at least 1 first-degree relative (mother, daughter, sister) with breast cancer before age 50, or 2 or more relatives with breast cancer at other ages.

Women with non-proliferative lesions had a slightly higher than normal risk of breast cancer only if they also had a strong family history of breast cancer. The risk was not higher than normal for these women if they had only a weak family history of breast cancer, or no breast cancer in the family. That point is important, the authors say, because many women fall into this category. In their study, 52% of the women who knew their family history of breast cancer were in this group.

The bottom line: "This study gives us a better understanding of which women who've had benign breast biopsies are at the greatest risk of developing breast cancer later in their lives," said Len Lichtenfeld, MD, deputy chief medical officer for the American Cancer Society, who was not involved in the research.

He advises such women to be sure they know what type of abnormal tissue the doctors found.

"Then she and her doctor can determine whether or not her risk of developing breast cancer is increased," he said. "And if it is increased, she should speak to her doctor and consider a consultation to determine whether she may be a candidate to take preventive drug treatment, which has been shown to reduce the risk of breast cancer in women at increased risk."

Citations: "Benign Breast Disease and the Risk of Breast Cancer." Published in the New England Journal of Medicine (Vol. 353, No. 3: 229-237). First author: Lynn C. Hartmann, MD, Mayo Clinic College of Medicine.

"Benign Breast Disease -- The Risks of Communicating Risk." Published in the New England Journal of Medicine (Vol. 353, No. 3: 297-299). First author: Joann G. Elmore, MD, MPH, University of Washington School of Medicine.