Breast Cancer Rates for California Counties

Women in some California counties are more likely to get breast cancer than women in other counties. Marin County has the highest rate for both early and later stage tumors; Imperial County has the lowest rate for early stage tumors; and the combined rates for Lassen, Modoc, and Plumas counties are the lowest for later stage tumors.

The reasons are unclear, but differences in the population levels of various ethnic groups in the counties are part of the explanation.

Comparisons between counties can be misleading. Some counties contain a wide variety of ethnic groups, income levels, and variations between city, suburban, and rural living. Others do not. For example, if the city of Beverly Hills were a county, it might have a rate similar to Marin County's. Since Beverly Hills is part of larger and more varied Los Angeles County, the Beverly Hills rate is mixed with rates of other LA county areas and not reported separately.

The rates on the facing page are the average number of cases per 100,000 women for the years 1995–1999. Some counties with small populations have been grouped together because they share similar ethnic mixes, similar geography, or historic connections.

Figure 6

Age-Adjusted Breast Cancer Rates

The figures in this section are adjusted for age. Adjusting for age allows the rates to reflect what they would be if all counties in California had the same age distribution. Older women are more likely to get breast cancer. Adjusting for age means that the differences between the counties are not due to one county containing more older women than another.

How This Research Was Done

The figures are rates based on the total number of cases of breast cancer reported to the California Cancer Registry for the years 1995–1999. For more about the Registry, or information about why the figures stop in 1999, see the introduction to this booklet. Information in this section comes from Chapter 8 of Breast Cancer in California, 2003, “Stage of Diagnosis of Female Breast Cancer in California, 1988–1999” by Paul K. Mills, Ph.D., M.P.H., and Ratnali Jain, M.B.B.S., M.S.