BREAST CANCER RESEARCH: The Marin Women’s Study

Mary Mockus, MD

Odds are that every physician in Marin County encounters breast cancer in their practice, either in their patients or in their patients’ family members and friends. Breast cancer strikes one in seven women in Marin (compared to one in eight women nationally) and is of great concern to our patients.

When the final numbers from the 1990 census were applied to Marin’s breast cancer rates, we stood out as a community with the highest rate of breast cancer in the United States. The media soon labeled Marin as the “breast cancer capital of the world.” All this attention led to town hall meetings, the hiring of epidemiologists at the Marin County Department of Health and Human Services (DHHS), and a Centers for Disease Control award of $217,000 to fund community breast cancer projects.

These efforts were followed by the formation of a National Scientific Advisory Committee that included national experts, members of the Marin General and Kaiser medical staffs, and local community groups such as Zero Breast Cancer. The committee addressed the meaning and validity of the data on breast cancer in Marin County. A thorough analysis of several decades of data established that the elevated rates of breast cancer in Marin were real and could not be explained by the age of the population, mammography rates, or other known risk factors in Marin women.

In April 2005, DHHS obtained more than $400,000 in federal research money to launch the Marin Women’s Study, a prospective effort to link individual risk factors with biospecimens and breast cancer outcomes. A local steering committee and 15 community groups partnered to plan the study; I serve as one of the principal investigators. The goal of the study was to obtain detailed risk factor information that could yield potentially immediate results as well as long-term, longitudinal data. Researchers developed an exhaustive questionnaire for Marin women on lifestyle, medical and personal history and paired the findings with screening mammography results.

The Marin Women’s Study began in fall 2008 and accrued participants for about 18 months. To date, 14,100 surveys have been received and analyzed. In addition, 8,000 of those participants have provided saliva samples to create a biorepository, which is processed and stored at the Buck Center. Specimens are available for hormone analysis and DNA testing, with results that can be paired with risk factor information and mammography results.

The generous participation of so many Marin women in the study has created a valuable resource that has caught the interest of cancer researchers worldwide. An adjunct to the study funded by the Avon Foundation includes specific analysis of the possible associations between hormones, reproductive history and increased breast density—a known risk factor for breast cancer. A second phase of the Avon study aims to develop a new risk model that links genes and the environment to other known cancer risk factors.

The first publication of Marin Women’s Study results appeared in the October 2010 issue of BMC Public Health.[1] Our research team found that a dramatic decrease in postmenopausal hormone replacement therapy during the 2000s was followed by a 33% decline in breast cancer cases. The real rates of breast cancer in Marin during the 2000s were about 50 cases per year less than the rates seen in the late 1990s, while at the same time the mammography rate remained unchanged.

The adjunct Avon study has shown that certain reproductive risk factors seem to affect breast density but not hormone levels. Gestational hypertension in particular—along with age at first pregnancy and nursing—were associated with breast density, but not with changed hormone levels (based on our saliva analysis). These findings suggest that the risk factors mentioned above may be creating persistent morphologic changes in the breast tissue that can be related to breast cancer risk.

Our next focus in data analysis will be on breast density as it relates to lifestyle factors such as life-course alcohol use, exogenous hormone use, and socioeconomic status. SNP (single nucleotide polymorphism) data from the saliva samples will be examined to see if genetic changes can explain the reproductive risk factors for increased or decreased breast density.

The Marin Women’s Study is an example of the power of cooperation and collaboration. The local steering committee includes Dr. Chris Benz of the Buck Institute; Rochelle Ereman, Dr. Mark Powell, Lee Ann Prebil and other members of the DHHS staff; Dr. Francine Halberg of Marin General; Fern Orenstein of Zero Breast Cancer; myself at Kaiser Permanente; and all Marin mammography centers regardless of hospital affiliation. We are all grateful to the 14,100 women of Marin County who have so generously given of their time.

As a physician investigator on this study, I feel a tremendous personal responsibility to the women of Marin, and I look forward to finalizing our data and sharing what we have learned with our wonderfully supportive community. More details and results of the Marin Women’s Study can be found on our website, marinwomensstudy.org.

Reference

1. Ereman RR, et al, “Recent trends in hormone therapy utilization and breast cancer incidence rates in the high incidence population of Marin County, California,” BMC Public Health, 10:228 (2010).

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Dr. Mockus, a surgeon at Kaiser San Rafael, is a principal investigator for the Marin Women’s Study.

Email: mary.b.mockus@kp.org