Although several studies suggest that women with denser breast tissue have an increased risk of breast cancer, a new study by Johns Hopkins researchers discredits breast density as a risk factor in and of itself, instead concluding that age and body fat, especially in the upper belly, contribute to the breast cancer seen in many patients.
"Many studies that link breast density to breast cancer risk used data from mammograms, which can't accurately measure breast density," says Wenlian Zhu, Ph.D., a research associate in the Johns Hopkins University School of Medicine and a member of the team reporting the study results online Oct. 21, 2015, in European Radiology. "Our research may help dispel the assertion that breast density alone is something women should be worried about with regard to their breast cancer risk, and it may help minimize confusion and unnecessary concern."
Breast density notification laws have been put into effect in 24 states. According to Zhu, such laws mandate that the presence of dense breast tissue and its potential to mask tumors be communicated to the patient. The breast density law in some states also mentions the "increased breast cancer risk associated with dense breast." The Centers for Disease Control and Prevention lists dense breasts by mammogram as one of the factors that increases breast cancer risk.
To confirm whether breast density is an independent risk factor for breast cancer, Zhu, working with colleagues from the Johns Hopkins Kimmel Cancer Center, examined 3-D, T1-weighted MRI breast scans done between 2007 and 2014 on 410 patients with invasive cancer in one breast, 73 patients with ductal carcinoma in situ, and 361 women with no evidence of breast cancer. The imaging technique used offers high contrast between fatty and dense glandular breast tissues, giving a more accurate measurement of breast density.
Along with information on breast density, the researchers also used MRI scans to assess adiposity using measurements of the fatty tissue thickness in the upper abdomen right beneath the breast. Then, investigators searched for links among breast cancer and breast density, body adiposity, and subjects' ages. The researchers found strong correlation between both age and adiposity with breast cancer. However, the correlation between breast cancer and breast density alone was insignificant.
Zhu says one likely explanation for their finding is that women with the densest breasts tended to be young and lean, both factors aligned with lower breast cancer risk. "Grouping all women with dense breasts into an elevated risk category could therefore be misleading and may cause unnecessary anxiety for many women," she says. "If further studies expand and confirm our research, we may be able to offer reassurance to many young and lean women with dense breasts."
Zhu cautions that her study did not specifically examine the interactions among age, adiposity and breast density for older women. Testing whether breast density is associated with breast cancer in this population will be the subject of future research, she says.
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