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Geographic Variations in Advanced Stage Breast Cancer in California, 1999-2003

Breast cancer is the most commonly diagnosed cancer among California women and the second most common cause of cancer-related death.  Most women diagnosed with breast cancer, however, are likely to survive particularly if the cancer is found at its earliest, most treatable stage.  Women with early stage disease (cancer that has not spread to other places beyond the breast) have a 97% probability of surviving 5 years.  However, once the cancer has spread beyond the breast to other parts of the body a woman’s likelihood of surviving 5 years decreases to 20%.1 

Women who receive regular breast cancer screening, regularly scheduled physical examinations and mammograms have the best opportunity to detect breast cancer at an earlier stage, when the likelihood of survival is much higher.   The American Cancer Society recommends regular breast cancer screening by mammography for all women starting at age 40.  The California Department of Public Health’s Every Woman Counts program provides breast cancer screening for women in the state who are medically uninsured or underinsured. 

The California Cancer Registry (CCR) routinely produces reports on cancer statistics for the state as a whole and by county.  State and county level statistics, however, do not show local variations in cancer that are of interest to communities for planning cancer control programs.  Data from the statewide, population-based CCR were analyzed to identify and map communities with a high percentage of breast cancer cases detected at an advanced stage compared to the state overall.  These maps are not intended to describe or compare geographic variations in breast cancer rates.

There can be many reasons for these variations among communities, including characteristics of the populations such as race, ethnicity, poverty, and education, as well as availability of and access to breast cancer screening.  This CCR information is being made available on the CCR website so that it may be used along with other locally relevant information by state and local officials to evaluate and target breast cancer early detection programs in their communities.

The report consists of 58 county maps in which the boundaries of sub-county neighborhoods, known as Medical Service Study Areas (MSSAs), are identified.  Accompanying each map is a data sheet that details the study results and provides some basic demographic data for each of the MSSAs.

Methods

Case Selection

  • The amount of breast cancer occurring in California – California’s breast cancer incidence - was based on cases of breast cancer diagnosed among California women aged 40 years and older between January 1, 1999 and December 31, 2003 and reported to the California Cancer Registry as of April 2006.  (The study only includes women aged 40 years and older because current guidelines recommend regular mammography screening for all women starting at age 40.)
  • This analysis was based on 97,933 cases.

Geographic Unit of Analysis (i.e., communities)

  • The California Office of Statewide Health Planning and Development (OSHPD) has defined 541 Medical Service Study Areas (MSSAs) in California.  MSSAs are aggregations of census tracts that make up “rational service areas” for primary health care and are used to identify medically underserved areas.
  • All cases were geocoded to a census tract based on the county and street address at time of diagnosis.
  • A MSSA code was assigned to each case based upon its census tract.

Definition of Advanced Stage

  • Using SEER summary stage criteria, cases were classified as early stage (in situ and localized) or advanced stage (regional and distant).

Comparison Group

  • The comparison group selected was non-Hispanic white women residing in high socioeconomic status (SES) neighborhoods. (A woman’s SES status was ascertained using census indicators of income, employment and education for the census block group of residence at diagnosis.)  Women in the high SES neighborhoods were chosen as the comparison group because they had the lowest proportion of advanced stage breast cancer (28%) compared to other race/ethnicity and income groups.

Analysis

  • The proportion of breast cancer diagnosed at advanced stage in each MSSA was compared to the proportion of breast cancer diagnosed at advanced stage in the comparison group.  Differences in the age distributions of the two groups were taken into consideration.
  • For mapping, communities with a significantly higher proportion of advanced stage cases were divided into two groups:  those where 40% or more of all breast cancer cases were diagnosed at advanced stage, and those where 30-39% were diagnosed at advanced stage.
  • Percentages of advanced stage breast cancer were only mapped in MSSAs that had at least 15 breast cancer cases diagnosed among women aged 40 years and older during the 1999-2003 time period.

Results

The proportion of breast cancer cases diagnosed at advanced stage was significantly elevated in 86 of the 541 MSSAs.  Of those, 30 MSSAs had 40% or more of all its cases diagnosed at advanced stage (Table 1 ). In 379 MSSAs the proportion of breast cancer cases diagnosed at advanced stage was not significantly different than the comparison group. In one MSSA the proportion of breast cancer cases diagnosed at advanced stage was significantly lower than the comparison group.  Results were not calculated for 75 MSSAs where less than 15 breast cancer cases were reported over the five-year period.

Conclusions

Geocoded registry data have been mapped to show communities with excess advanced stage breast cancer compared to the rest of the state. These maps are now available on the California Cancer Registry website. The links to each California county map can be found in the left column under GIS Breast Cancer Quick Links; each map shows the MSSAs within the county and the percentage of advanced stage breast cancer in the MSSAs.  Accompanying each map is a sheet that details the study results and the demographics for each MSSA.

If you would like more detail about the study and/or the maps, please contact Holly Hodges at the California Cancer Registry.  Phone:  916-779-2662.  Email:  hhodges@ccr.ca.gov

References

  1. American Cancer Society, California Division and Public Health Institute, California Cancer Registry. California Cancer Facts and Figures 2008. Oakland, CA: American Cancer Society, California Division, September 2007.