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

Colorectal cancer (CRC) is the third most commonly diagnosed cancer among California men and women and the third most common cause of cancer-related death for each sex. The California Cancer Registry estimates that in 2008 about 14,100 Californians will be diagnosed with CRC and about 5,200 will die of the disease. When CRC is found early, the chance of survival is quite good. Individuals diagnosed with CRC at an early stage (i.e., when the cancer is confined to the colon or rectum) have a 90% probability of surviving five years. However, once the cancer has spread beyond the colon or rectum (i.e., to nearby tissue or lymph nodes) a person's likelihood of surviving five years decreases to 66%. If CRC is diagnosed at an advanced stage (i.e., when the cancer has spread to other parts of the body), the probability of surviving five years is 9%.

Effective screening tests that allow for the early detection of CRC exist. The American Cancer Society (ACS) recommends that adults at average-risk for CRC begin to get screened at age 50. However, individuals with certain risk factors that increase their chance of developing CRC may want to begin screening at an earlier age or be screened more often. Each person should discuss their individual risk of getting CRC, and their screening options, with their health care provider. For more specific information on CRC screening guidelines, visit the American Cancer Society's website at www.cancer.org or call 1-800-227-2345.

Although early diagnosis of CRC through screening improves outcomes and reduces mortality, CRC screening is underutilized. According to the 2006 California Behavioral Risk Factor Survey (BRFS), the majority of California adults aged 50 years and older reported that they have not had any of the following CRC screening tests in the last five years - a sigmoidoscopy, a colonoscopy, or a fecal occult blood test using a home kit. Another indirect measure of screening utilization is the proportion of CRC diagnosed at advanced stage. Of all the CRC cases included in this study, the majority (54%) were diagnosed at advanced stage. We would expect a much smaller proportion of cases to be diagnosed at advanced stage if people were getting screened in accordance with the established guidelines.

The California Cancer Registry (CCR) routinely produces reports on cancer statistics for the state as a whole (www.ccrcal.org) 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 CRC cases diagnosed at advanced stage compared to the state overall.

There can be many reasons for variations in the percentage of CRC diagnosed at advanced stage among communities, including characteristics of the population such as race, ethnicity, poverty, and education as well as the availability of and access to CRC screening. This 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 CRC early detection programs in their communities.

The report consists of 58 county maps in which the boundaries of sub-county communities, 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 information for each MSSA.

Methods

Case Selection

  • The amount of colorectal cancer (CRC) occurring in California - California's colorectal cancer incidence - was based on new cases of CRC diagnosed among California residents aged 50 years and older between January 1, 1999 and December 31, 2003 and reported to the California Cancer Registry (CCR) as of October 2005. (The study only includes persons aged 50 years and older because current guidelines recommend screening begins at age 50 for persons at average-risk for colorectal cancer.)
  • This analysis was based on 50,478 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, which are groups 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, distant, or unknown stage). For more detailed information on SEER summary stage criteria go to www.seer.cancer.gov.

Comparison Group

  • The comparison group selected was non-Hispanic white persons residing in high socioeconomic status (SES) neighborhoods. (A person's SES status was ascertained using census indicators of income, employment, and education for the census block group of residence at diagnosis). Non-Hispanic white persons in high SES neighborhoods were chosen as the comparison group because they had the lowest proportion of advanced stage CRC (55.8%) compared to other race/ethnicity and income groups.

Analysis

  • The proportion of CRC diagnosed at advanced stage in each MSSA was compared to the proportion of CRC diagnosed at advanced stage in the comparison group. Differences in the sex and age distributions of the two groups were taken into consideration.
  • For mapping, communities with a significantly higher proportion of advanced stage CRC cases were divided into two groups: those where 70% or more of all CRC cases were diagnosed at advanced stage, and those where 60-69% were diagnosed at advanced stage. Communities with a significantly lower proportion of advanced stage cases were also mapped if less than 50% of all CRC cases were diagnosed at advanced stage.
  • Percentages of advanced stage CRC were only mapped in MSSAs that had at least 15 CRC cases diagnosed among individuals aged 50 years and older during the study period.

Results

The proportion of CRC cases diagnosed at advanced stage was significantly elevated in 87 of the 541 MSSAs. Of those, 17 MSSAs had 70% or more of all CRC cases diagnosed at advanced stage and 70 MSSAs had 60-69% of all CRC cases diagnosed at advanced stage. In 331 MSSAs the proportion of CRC cases diagnosed at advanced stage was not significantly different than the comparison group. In 12 MSSAs the proportion of CRC cases diagnosed at advanced stage was significantly lower than the comparison group. Results were not calculated for 111 MSSAs where less than 15 CRC cases were reported over the five-year period.

Conclusions

Geocoded registry data have been mapped to show communities with an excess of CRC cases diagnosed at advanced stage. 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 CRC Resources.; each map shows the MSSAs within the county and the percentage of advanced stage CRC in the MSSAs. Accompanying each map is a table that details the study results and the demographic information for each MSSA.

If you would like more details about the study and/or the maps, please contact Brenda Hofer at the California Cancer Registry. Phone: (916) 779-0300