As density drops over time, so does risk, one study finds,,
WEDNESDAY, April 21 (HealthDay News) -- Having dense breasts has long been known to increase a woman's risk for breast cancer, and new research confirms that a decline in breast density over time does, in fact, decrease that risk.
New research also has found that women taking hormone replacement therapy are more likely to experience an increase in breast density, a finding consistent with previous research that found women taking the hormones had a 24 percent increased risk for breast cancer.
Both findings were to be presented Tuesday and Wednesday in Washington, D.C., at the annual meeting of the American Association for Cancer Research.
"Over 50 studies have shown that breast density is a strong risk factor for breast cancer," said Celine M. Vachon, an associate professor of epidemiology in the College of Medicine at the Mayo Clinic, in Minnesota. "Our study is one of the first to examine changes over time," Vachon said.
A very dense breast has less fat than glandular and connective tissue. Mammogram films of high-density breasts are more difficult to read and interpret than those of less dense breasts.
Vachon and her fellow researchers followed 19,924 women older than 35 who had never had breast cancer and looked at breast density changes and cancer diagnoses over time.
From that group, they randomly picked a sample of 219 women who developed breast cancer during the six-year follow-up period and 1,900 who did not. Women with breast cancer were more likely to have extreme breast density -- the highest of four categories -- at the start of the study, with 16 percent in the very dense category, compared with 14 percent of those who remained cancer-free.
Those who developed cancer were somewhat less likely than the other women to have a reduction in density of one category or more, with 37 percent of those with bre
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