Improving cancer incidence estimates for American Indians in Wisconsin.

OBJECTIVES The purpose of this study was to improve the measurement of cancer incidence among American Indians in Wisconsin and compare incidence rates with state and national incidence rates. METHODS The Wisconsin Cancer Reporting System (WCRS) entered into a data linkage project with CDC and the Indian Health Service (IHS) to improve classification of American Indian cancer cases in Wisconsin. WCRS data were linked to IHS patient registration files to identify American Indian cases that were misclassified as a non-Indian race for the years 1998-2002. American Indian age-adjusted rates and rate ratios for major cancer sites were compared before and after the linkage, and with statewide and national rates. RESULTS The age-adjusted incidence rate for all cancer among American Indians increased from the pre-linkage rate of 386.3 per 100,000 to the post-linkage rate of 471.7 per 100,000, a statistically significant increase. The post-linkage rate was over twice the comparable Surveillance Epidemiology and End Results (SEER) national rate among American Indians at 233.6 per 100,000. Post-linkage American Indian incidence rates for male colorectal and female lung cancers were higher than those for the state average. CONCLUSIONS In contrast to earlier data, the linkage results show that American Indians had similar cancer incidence compared to the general population in Wisconsin, and over twice as high as national SEER American Indian rates. Post-linkage rates resulted in more accurate site-specific and geographically focused cancer incidence rates to help target the national and state priorities of addressing disparities among American Indians.