Important Breast Cancer News for Marin Women

by Rochelle Ereman

October is Breast Cancer Awareness Month, and it’s important to share what we've  learned about the high rates of breast cancer in Marin County.

The question has been asked for years: Why do women in our county have much higher rates of cancer than in other parts of the state, the country and the world? There has been a great deal of speculation about potential causes:  Was there something in the water? Was cancer caused by something we used or consumed?  If so, how could any of these be so uniquely different in Marin to cause so much more breast cancer here?

The Marin Women’s Study was established to ask and try to answer these questions. Launched in 2006 by the Marin County Department of Health and Human Services under the leadership of Dr. Larry Meredith, the Marin Women’s Study is a community-based project established to monitor changes in breast cancer and breast density as well as personal, environmental and biological risk factors among women living in Marin County.  The study is funded by the Centers for Disease Control and Prevention (CDC) and is supported by Congresswoman Lynn Woolsey and Senator Barbara Boxer.

Approximately 30 percent of the total population of women ages 50+ in this county, and up to 75 percent of total mammography patients, are participants in the study.  These remarkable rates are invaluable to our work and the potential for important findings regarding breast cancer.  The first major results from the Marin Women’s Study were published last year, and the findings were dramatic:  the use of combined estrogen/progesterone hormone replacement therapy plummeted after widespread news of potential impacts. This was followed by a sharp decline in the rates of invasive breast cancer.

By 2004, breast cancer rates in our county had dropped to 345 cases per 100,000—a striking 33.4 percent reduction between 2001 and 2004.  This was equivalent to a decline of 50 cases per year in Marin County, or 150 cases over the three year period.  The study also found that while overall hormone therapy was not higher in Marin County than the rest of California, many more women in Marin had been taking the combined estrogen/progestin hormones rather than estrogen only.  In fact, Marin County ranked fourth highest of 41 counties reporting in the state in the use of the combined hormones. 

This led researchers to ask why-- and we found that Marin had one of the lowest rates of hysterectomies in California. (Just over 23 percent of Marin County women over 50 have had a hysterectomy compared to almost 56 percent in Sutter County.)  Women who have had a hysterectomy are usually prescribed estrogen only, while women who have not had the procedure were generally advised to take the combined hormone therapy.

Our results to date do not mean that combined hormone therapy use was the sole cause or explanation for the unusually high breast cancer rates in Marin, nor do we know if rates will continue as observed in the study. Given these findings, we recommend you discuss the potential risks with your physician if you are currently taking, or are considering adopting, a hormone therapy regimen.

Thanks to the Avon Foundation for Women, the women of Marin County and an outstanding research team, the study has made important initial findings.  It also has an invaluable resource of questionnaire data on nearly 14,000 women and biospecimens on nearly 8,500 women which can be used locally and by researchers all over the world.  However, there is much more to learn.  For instance, we are working to understand why some women with risk factors get breast cancer while others don't.

As the principal investigator for the study, I am so pleased that our data have been useful in explaining changes in breast cancer incidence in our community. We are committed to ongoing monitoring and analysis of the risk factors, and we continue to seek funding to continue this critical research.  Both the findings of our research, and the new questions before us, are very important for public health—and your health.

Rochelle Ereman is the head of the Epidemiology Program with the Marin County Department of Health and Human Services and serves as the principal investigator for the Marin Women’s Study.  Research partners include:  Kaiser Permanente, Marin General Hospital, The Buck Institute for Age Research, Cancer Prevention Institute of California (formerly Northern CA Cancer Center), UCSF and Zero Breast Cancer. 

For more information visit www.marinwomensstudy.org  (to view the journal article click on “1st Scientific Publication, May 2010”). For prevention information go to www.cdc.gov/cancer/breast.