Breast Density Is a Strong Risk Factor for Breast Cancer

Age and family history also play important roles for all women

WEDNESDAY, Sept. 6 (HealthDay News) -- In the mix of risk factors for breast cancer, breast density carries a strong additional risk, but whether reduction in density reduces that risk remains unknown, according to research published in the Sept. 6 issue of the Journal of the National Cancer Institute.

William E. Barlow, Ph.D., of Cancer Research and Biostatistics in Seattle, and colleagues evaluated 2,392,998 screening mammograms from over one million women who had a mammogram in the previous five years. Within one year of a screening mammogram, breast cancer was diagnosed in 11,638 women, for a rate of 4.86 breast cancers per 1000 screening mammograms.

The researchers constructed separate logistic regression models for premenopausal and postmenopausal exams. Risk models were constructed with 75 percent of the data and validated with the rest. Mammograms from women aged 45 to 54 years with unknown menopausal status were excluded. The remaining mammograms were classified as premenopausal (25.7 percent), or postmenopausal (74.3 percent). There were 1,726 breast cancers among premenopausal women, for an absolute rate of 3.04 per 1000 screening mammograms and 9,300 breast cancers among postmenopausal women, for an absolute rate of 5.66 per 1000 screening mammograms.

Statistically significant risk factors in premenopausal women included age, breast density, family history and prior breast procedure; in postmenopausal women, age, breast density, race, ethnicity, family history, prior breast procedure, body mass index, natural menopause, hormone therapy, and prior false-positive mammogram were statistically significant.

"Breast density was strongly associated with breast cancer risk, with women with the highest breast density having a risk of 3.16 compared with those with the lowest density even after adjustment for several factors including age and body mass index," the authors conclude.

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