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University of Minnesota Researchers Find Evidence of Genetic Link to Breast Density

University of Minnesota Researchers Find Evidence of Genetic Link to Breast Density

Researchers at the University of Minnesota Cancer Center have found evidence that mamographic breast density, a measure of the relative proportions of fat, connective tissue, and glandular epithelial tissue in the breast that is a strong, independent predictor of breast cancer risk, is genetically influenced. The study, published in the April 16th Journal of the National Cancer Institute, also suggests that 12% of the population has a genetic mutation that results in a breast density twice that of women without the mutation.

"It isn't known how high breast density increases the risk of breast cancer," said lead investigator Thomas Sellers, associate professor of epidemiology and associate director of the Cancer Center. "But the risk is considered second only to the risk incurred by mutations in the BRCA1 and BRCA2 genes."

The researchers obtained routine mammograms and a variety of health-related data from 1,370 women from 258 different Minnesota families. The study population included 65 mother-daughter pairs and 275 sister-sister pairs. All of the women were related, either genetically or by marriage, to an original group of 544 breast cancer patients seen at the University of Minnesota between 1944 and 1952. Sellers and colleagues are studying these families as part of the Breast Cancer Family Cohort study.

Breast Density Partly Modifiable

Sellers says that the study is significant because the researchers were able to separate out other risk factors, such as waist-to-hip ratio, physical activity, hormone replacement therapy, and number of live births, to detect a Mendelian dominant inheritance pattern (a pattern where only one copy of the mutated gene is necessary to transfer the trait to offspring). They were unable, however, to completely eliminate the possibility of a recessive pattern, which would require more than one copy of a gene to produce a trait. However, if breast density is, indeed, controlled by a dominant gene, about 12% of the population would be expected to carry a form of the gene that results in a breast density about twice that of the rest of the population. "The good news is that while breast density risk factor is partly genetic, it's also shaped by the environment, and so can be modified," Sellers said.

In previous studies, Sellers and colleagues have reported on potential risk factors for breast cancer, including waist-to-hip ratio, fat in the diet, and the connection between breast cancer in women and prostate cancer in men. These finding stem from the Iowa Women's Study, an ongoing health study of more than 40,000 women in Iowa.

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