Marin County, Calif., has one of the highest rates of breast cancer in the world, a fact that scientists know has nothing to do with the land itself but with some other, unknown factor.
A new study that analyzed mouth buccal cell samples stored frozen at the University of California, San Francisco (UCSF) suggests what this factor may be: a genetic trait present among women within the county’s predominantly white population.
In an article published online this week by the Journal of the American College of Surgeons, which will appear in the November 2012 print issue, surgeon scientist Kathie Dalessandri, MD, FACS and colleagues at UCSF and the company InterGenetics Inc. in Oklahoma City describe how, in a small, retrospective pilot study involving the mouth cells from 338 women living in Marin, slight variations within the DNA of a human gene for vitamin D receptor were associated with breast cancer risk.
“While the findings must be validated in a much larger, prospective study,” Dalessandri warned, “we found that women who were at high risk for breast cancer were 1.9 times more likely to have a specific vitamin D receptor variation than the general population.”
A larger, collaborative prospective study in Marin County is ongoing, spearheaded by the Marin County Department of Health and Human Services. This study includes an examination of breast cancer risk on a scale involving thousands of women.
For now, Dr. Dalessandri said, there is no clear-cut advice on the level of vitamin D needed for breast cancer prevention, but variations in the vitamin D receptor may be an important modulator of risk.
The discovery does not rule out that there may be other factors involved in the elevated breast cancer risk in Marin County, said Dalessandri, but it gives an important clue moving forward.
After More than a Decade, New DNA Secrets
The first major study to look at the question of why women in Marin County are at higher risk for breast cancer was led by UCSF cancer epidemiologist Margaret Wrensch, MPH, PhD
, and Georgianna Farren and colleagues from Marin Breast Cancer Watch.
Published in 2003, that study compared 285 women with breast cancer in Marin with 286 local women who did not have the disease, and examined traditional risk factors such as risk of breast cancer based on a woman’s age at the time of diagnosis of breast cancer, age when menstruation began, age at first live birth, history of breast cancer in first degree relatives, history of breast irradiation, history of benign breast biopsies, and use of hormone replacement therapy that may have accounted for the difference—as well as environmental, lifestyle and nutritional factors.