TUESDAY, Nov. 21, 2006 (HealthDay News) -- A woman's risk for breast cancer as she grows older appears strongly linked to the natural process of lobular regression, Mayo Clinic researchers have concluded.
Lobular regression, also known as involution, occurs as most women's milk-producing glands (lobules) start to shut down with age. Since it's believed that breast cancer originates in the lobules, the Mayo research showed that a reduction in the size and number of lobules reduced the cancer risk.
The study, involving more than 8,700 women, found that those with benign breast disease and little or no involution were twice as likely to develop breast cancer compared to women whose breast glandular tissues had been replaced with connective and fatty tissue.
"Our study is the first to establish that the extent of breast involution relates directly to risk for breast cancer," oncologist and lead investigator Dr. Lynn Hartmann said in a prepared statement.
The researchers also found that 53 percent of women age 70 and older had complete involution.
Women who had never used hormone replacement therapy (HRT) were more likely to have complete involution than those who did have HRT (22.9 percent vs. 20.3 percent), the researchers add. Twenty-seven percent of women who had had no children had complete involution, compared to 18 percent of women who had more than three children.
Breast-feeding had no impact on involution, the study found.
The findings were published in the Nov. 15 issue of the Journal of the National Cancer Institute.
The study provides doctors with another important factor to help them predict a woman's risk for breast cancer, Hartmann said.
The U.S. National Cancer Institute has more about breast cancer risk.