Abstract PL08-02: Colorectal cancer health disparities: Role of racial disparities in stage.
Authors: Robbins Anthony S. 
Published: August 2014

Colorectal cancer (CRC) is the second leading cause of cancer death in the US. Over the last four decades, advances in screening, early detection, and treatment have led to large reductions in age-adjusted CRC mortality rates. However, as the overall CRC mortality rate has declined, disparities in CRC mortality have worsened. For example, using data from the nine original registries in the Surveillance, Epidemiology, and End Results Program (denoted as SEER 9), in 1975–79, age-adjusted CRC mortality rates for whites and blacks were 29.0 and 29.7 per 100,000, respectively. However, during 2005–09, the corresponding rates were 15.1 and 23.1, respectively (53.0% higher rate in blacks). (All incidence and mortality rates in this presentation are per 100,000 population and age-adjusted to the 2000 US Standard Population. Stage at diagnosis was grouped into local, regional, distant, and unstaged, according to SEER Summary Stage guidelines.)

Cancer mortality rates are driven by trends in stage-specific incidence rates and stage-specific survival. Because of the poorer survival for advanced disease, decreases in the incidence of regional and distant stage, and increases in survival for advanced disease have particularly favorable impacts on the mortality rate. Overall and stage-specific incidence rates are affected by changes in risk factor prevalence as well as screening and early detection programs, while stage-specific survival rates are primarily affected by improvements in treatment.

This presentation describes trends for whites and blacks in the US from 1975 to 2009, using data from SEER 9, which covers approximately 10% of the US population. Race-specific trend data are presented for CRC mortality, incidence, and 5-year relative survival rates (relative survival is the ratio of observed to expected survival and represents the probability of surviving cancer for a specific period of time).

Between 1975–79 and 2005–09, for whites, overall CRC incidence decreased from 62.3 to 44.4 (–28.7%), while for blacks, overall incidence only decreased from 58.7 to 55.5 (–5.5%). For whites, stage-specific changes in incidence during this time were as follows: localized, from 20.9 to 19.0 (–9.1%); regional, from 22.2 to 15.1 (–32.0%); distant, from 12.9 to 8.3 (–35.7%); and unstaged, from 6.2 to 2.0 (–67.7%). For blacks, corresponding stage-specific incidence changes were: localized, from 17.9 to 21.9 (+22.3%); regional, from 19.5 to 17.0 (–12.8%); distant, from 14.8 to 13.1 (–11.5%); and unstaged, from 6.4 to 3.6 (–43.8%).

Changes in stage-specific 5-year relative survival were also examined, using data from CRC cases diagnosed during 1975–77 and cases diagnosed during 2002–08; all cases were followed through December 2009. For whites, the changes in stage-specific survival were as follows: localized, from 82.2% to 91.1% (+10.8%); regional, from 53.8% to 72.2% (+34.2%); distant, from 5.6 % to 12.6% (+125.0%); and unstaged, from 31.3 % to 28.9% (+%). For blacks, corresponding changes in survival were: localized, from 76.5% to 85.9% (+12.3%); regional, from 50.0% to 65.4% (+30.8%); distant, from 6.3% to 8.3% (+31.7%); and unstaged, from 34.9% to 32.6% (6.6%).

These data suggest that both decreases in stage-specific incidence and increases in stage-specific survival have played important roles in the downward trend in CRC mortality rates, particularly for whites. With respect to stage-specific incidence, whites experienced much larger decreases in the incidence of advanced (regional and distant) disease, particularly distant stage. As noted above, 5-year survival for distant stage is very poor (from SEER-9, 13% for whites and 8% for blacks in the most recent time period). Whites also experienced larger increases in stage-specific survival, particularly for distant stage, where their survival more than doubled over this four-decade period.

These data suggest that advances in screening, early detection, and treatment of CRC have not equally benefitted whites and blacks, and that these inequities have contributed to worsening racial disparities in CRC mortality.

Citation Format: Anthony S. Robbins. Colorectal cancer health disparities: Role of racial disparities in stage. [abstract]. In: Proceedings of the Fifth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2012 Oct 27-30; San Diego, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(10 Suppl):Abstract nr PL08-02.