Incidence of and Trends in the Leading Cancers With Elevated Incidence Among American Indian and Alaska Native Populations, 2012–2016

Stephanie C. Melkonian; Hannah K. Weir; Melissa A. Jim; Bailey Preikschat; Donald Haverkamp; Mary C. White

Disclosures

Am J Epidemiol. 2021;190(4):528-538. 

In This Article

Methods

Cancer incidence data came from the National Program of Cancer Registries (NPCR) of the Centers for Disease Control and Prevention and the Surveillance, Epidemiology and End Results (SEER) Program of the National Cancer Institute.[2,3] During the period covered by this study (2012–2016 for rate and 1999–2016 for trends), tumor histology, tumor behavior, and primary cancer site were coded according to the third edition of the International Classification of Disease for Oncology (ICD-O-3) and classified according to SEER site categories.[4]

To reduce racial misclassification of AI/AN populations, cancer registry data were linked with the Indian Health Service (IHS) patient registration database by using previously established and validated techniques that improve accuracy of cancer incidence estimates among the AI/AN population.[5,6] Each year, NPCR- and SEER-funded central registries submit data on cancers diagnosed during the most recent year to the respective program.

Incidence data from registries meeting rigorous quality control standards were combined into an analytical file, US Cancer Statistics.[7] By combining these registries, we have 100% coverage of the AI/AN population. To improve racial classification of AI/AN populations, we restricted analyses to purchased/referred care delivery area (PRCDA) counties, which contain, or are adjacent to, federally recognized tribal lands. Restricting to PRCDA counties provides more accurate correction for racial misclassification of the AI/AN population than other counties.[5,6] Approximately 53% of the AI/AN population resides in these counties (Web Figure 1, available at https://doi.org/10.1093/aje/kwaa222).

Population estimates that were used as denominators in the rate calculations were produced by the US Census Bureau. In a previous report, the updated, bridged, intercensal population estimates overestimated AI/AN populations of Hispanic origin.[8] In the present study, all analyses were limited to non-Hispanic AI/AN populations to avoid underestimation of incidence rates among the AI/AN population. Non-Hispanic White was chosen as the reference population. For conciseness, the term "non-Hispanic" was omitted when discussing both groups in this study.

Cancer incidence rates for the 15 most common cancers were expressed per 100,000 population and were directly age-adjusted, by using 19 age groups, to the 2000 US standard population using SEER*Stat software, version 8.3.2.[9] Using the age-adjusted incidence rates, we calculated age-standardized rate ratios for the years 2012–2016 among the AI/AN population, with the White population as reference for each region. The leading cancer types with elevated incidence were identified for each region and sex separately. From the 15 most common cancers overall, the leading cancers with elevated incidence were identified as cancers with a rate ratio of >1 (P < 0.05) and ranked based on rate ratio. The 6 geographic regions and PRCDA counties have been described previously[1] and are shown in Web Figure 1. They include Alaska, the Northern Plains, Southern Plains, Pacific Coast, East, and Southwest. Rate ratios comparing men versus women were also calculated.

Long-term cancer incidence trends during 1999–2016 (average annual percent change, or AAPC) were estimated by joinpoint regression for the leading elevated cancers in each region. Trends for the entire period were estimated by using software developed by the National Cancer Institute (Joinpoint Regression Program, version 4.3.10).[10]

To estimate the number of excess cancers experienced among AI/AN populations, the 5-year, age-specific cancer incidence rates among the White population were applied to the corresponding population estimates among the AI/AN populations, according to sex, for the cancer types with elevated incidence in each region during 2012–2016. Excess cancers were calculated as observed minus expected cases for each cancer type, similar to previous studies that have examined elevated incidence and death.[11,12] The observed-to-expected ratio was calculated to determine relative elevated incidence between the AI/AN and White populations.

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