Regional differences in cancer incidence among American Indians/Alaska Natives in the Pacific Northwest

Background: In the northwest, cancer is a leading cause of morbidity and mortality for American Indians and Alaska Natives (AI/AN). Misclassification of AI/AN race in state cancer registries causes cancer burden to be underestimated. Methods: We corrected race coding in the cancer registries of Idaho, Oregon, and Washington using probabilistic record linkage to a file derived from Indian Health Service patient enrollment records. Using linkage-corrected race data, we examined cancer incidence rates and leading sites across the three-state region, comparing AI/AN to Non-Hispanic White (NHW) race. Results: Record linkage increased case ascertainment of AI/AN cancers by 13%. Across the region, cancer incidence would have been significantly underestimated without correction of race (age-adjusted rate, 2000-2005 = 314 [95% CI: 297 – 332] per 100,000 pre-linkage, vs. 370 [95% CI: 352 – 390] per 100,000 post-linkage). Idaho AI/AN had significantly lower rates of all-site invasive cancer than either Oregon or Washington, though rates for NHW were similar across the states. Several regional differences were noted, including a relatively high incidence of blood cancers among Idaho AI/AN, disproportionate lung cancer rates among Oregon females, and disparities in colorectal cancer stage-at-diagnosis compared to NHW. Conclusions: The correct classification of race is a crucial factor in cancer surveillance, and can reveal regional differences even within a relatively small area. Improved understanding of local cancer trends can help inform states and tribal communities in appropriate prevention and early detection efforts.