Most women with breast lumps or other abnormalities that turn out to be non-cancerous do not face a substantially greater risk of developing breast cancer later, especially if they have little family history of the disease, a reassuring study found.
However, certain “benign” growths are not so harmless and may be precursors to cancer, it also found. Women with these may want to consider surgery or tamoxifen to lower their risk, doctors say.
The study was one of the largest to look at cancer risk according to the types of benign growths women had. It involved 9,087 women biopsied from 1967 to 1991 at the Mayo Clinic in Rochester, Minn. The findings were reported in Thursday’s New England Journal of Medicine.
The information could be useful to a large number of women. In a decade of having mammograms, one out of five women will have a biopsy, and most biopsies will reveal benign growths, two specialists wrote in an accompanying editorial.
Overall, such women are 56 percent more likely to develop cancer during the next 15 years, the study found — the same conclusion previous ones reached. But the new work shows how much this risk varies — from very little to more than four times normal — depending on what the growths look like under the microscope.
Type of growth is key
“Many of these women are not at significantly increased risk for breast cancer, but it’s important that they know what their pathology showed” about the type of growth they had, said Dr. Lynn Hartmann, the Mayo doctor who led the work.
More than 1 million American women each year are diagnosed with benign breast conditions — suspicious clumps of cells, fluid-filled sacs called cysts, or solid masses called tumors.
In the Mayo study, 707 out of the 9,087 women with such conditions developed breast cancer, typically about a decade later.
Two-thirds of the benign growths studied were made up of cells that were not rapidly dividing. Previous studies have disagreed on how much cancer risk women with these “nonproliferative” growths face. The Mayo study found it was only 27 percent higher than that of women without such growths. (The comparison group was 1.5 million women from Iowa’s general population.)
Thirty percent of women in the Mayo study had actively growing abnormalities; they had an 88 percent greater chance of later developing cancer.
About 4 percent of the women had the most worrisome growths, made up of highly abnormal-looking cells that were actively growing. These women had a 324 percent greater risk of developing cancer.
'In the eye of the beholder'
Dr. Susan Love, a Los Angeles breast cancer surgeon, author and researcher, said a big problem is that a pathologist’s judgment that cells look “abnormal” is extremely subjective. “It’s in the eye of the beholder,” she said.
Highly abnormal growths should be removed even when they are technically benign, said Dr. Julia Smith, director of breast cancer screening and prevention at the NYU Cancer Institute.
In an editorial, Gerd Gigerenzer of the Max Planck Institute for Human Development in Berlin and Dr. Joann Elmore of the University of Washington School of Medicine in Seattle urged doctors to portray these risks in less scary-sounding terms to patients.
A 27 percent increase in risk means that about 6 women out of 100 would develop breast cancer instead of the 5 that would have been expected to, they write. Having the worst type of growth raises the breast cancer risk to about 19 out of 100.
All are lower than the risk faced by women with BRCA gene mutations that predispose them to breast cancer, doctors note.
Age also made a difference in risk. Women diagnosed with benign breast growths before they were 40 had greater chances of developing breast cancer than those who were older when theirs were found.
Family history also mattered. Women with abnormalities that weren’t actively growing and who had few or no close relatives with breast cancer had no increased risk of the disease themselves.
The study did not settle one important question: whether benign lumps gradually turn into cancers or are just signs that the woman has a higher background risk and is therefore more likely to develop cancer in the rest of her breast tissue.
In the Mayo study, cancers were slightly more likely to develop in the same breast versus the opposite one. “This finding suggests that precursors to breast cancer exist in benign breast disease,” the authors write.
Also in the journal, Dr. Richard Santen of the University of Virginia and Dr. Robert Mansel of the University of Wales note that women who take estrogen for more than eight years after menopause are about 70 percent more likely to develop benign breast growths than women who do not take hormones.