During 2001, portions of Napa and American Canyon were identified as Bay Area locations with high rates of invasive breast cancer. In subsequent years, the rate was about the state average.

Analysis conducted by the California Breast Cancer Mapping Project identified four “areas of concern” during the research period of 2000 to 2008. These areas, which included Marin County and the South Bay, had invasive breast cancer rates 10 to 20 percent higher than the state average.

The research didn’t say why these locations had higher rates of breast cancer.

“It is difficult to know precisely how to interpret the findings of this report at this point, but we feel they do warrant further consideration,” said Dr. Jennifer Henn, an epidemiologist with Napa County Public Health.

Henn pointed out that although the mapping project identified areas of American Canyon and Napa as having elevated levels of invasive breast cancer, these rates were only elevated for one of the nine years examined in the study.

“For the other 8 years of data examined, rates of invasive breast cancer did not differ significantly from the statewide average,” Henn said.

According to the research, rates were elevated in Napa County only in 2001.

Information for the project was collected from the California Cancer Registry, which described the numbers of invasive breast cancer cases among women by age, year of diagnosis, and census tract of residence at the time of diagnosis, according to the California Breast Cancer Mapping Project.

Normally, breast cancer rates are reported at the county level. But using U.S. Census Tract data identifies areas that are sometimes smaller than counties or extend across county boundaries.

The southern end of Napa County, for example, was included in the larger “area of concern” for the North Bay. Parts of Marin, Sonoma, Solano, Contra Costa and Alameda counties also were highlighted on the map.

Breast cancer has genetic, behavioral and environmental causes that likely interact with each other in complex ways, Henn said. It is not known why women living in certain areas may be at higher risk.

The Napa County Health and Human Services Agency, hospitals, healthcare providers and numerous community-based organizations are working together to develop a public health assessment and health improvement plan for the county, Henn said. Breast cancer data, including findings from this recent study, will be included in that assessment.

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