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

Discussion

This study provides a comprehensive overview of the leading cancer types with elevated incidence among the AI/AN population, by region, for the years 2012–2016. The cancers identified as excess cancers in this study are driving cancer disparities in AI/AN populations and have been shown to contribute to cancer-related disparities in other underrepresented populations.[13–15] The present study confirms prior findings that showed substantial regional variation in cancer incidence rates among the AI/AN population.[1,16] These findings provide further evidence that data aggregated across cancer sites or by region mask important differences in cancer incidence, both within the AI/AN population and between the AI/AN and White population. Liver, stomach, kidney, lung, and colorectal cancers were among the cancers consistently elevated across several regions among the AI/AN population. This study estimated that nearly 5,200 cases of cancer in the AI/AN population were potentially avoidable during 2012–2016 among AI/AN populations in the 6 study areas if racial disparities had not existed in cancer incidence.

Liver cancer was a leading cancer with elevated incidence among AI/AN populations in nearly every region. Incidence rates were as much as 4 times higher than rates among the White population among both AI/AN men and women, confirming previous findings.[17] The prevalence of hepatitis C virus (HCV) infection, a known risk factor for liver cancer, is higher among the AI/AN population than among the non-Hispanic White population.[17,18] To increase screening for HCV among the AI/AN population in the Southern Plains, the Cherokee Nation Health Services implemented a clinical decision support tool within the health records for primary care physicians, targeting individuals at high risk of liver cancer. This effort resulted in a nearly 14% increase in the number of eligible individuals receiving HCV screening during 2012–2015, and nearly 90% of the individuals subsequently treated after HCV diagnosis achieved a cure.[19] Other efforts include collaborations between IHS and Project ECHO (Extension for Community Healthcare Outcomes) aimed at improving HCV-related care for the AI/AN population through teleconsulting and "telementoring" partnerships between specialists and providers in rural and underserved communities.[20]

This study also confirmed previous findings about the elevated incidence of kidney cancer among the AI/AN population.[21] Increases in kidney cancer incidence have been linked with rising rates of obesity.[21–23] Previous studies suggested that smoking and hypertension might also play roles in elevated kidney cancer rates.[24] These few known risk factors for kidney cancer are unlikely to fully explain the observed geographic variation in kidney cancer incidence or the elevated incidence rates among the AI/AN population. Additional studies can help better illuminate the factors driving differences in kidney cancer incidence between the AI/AN and White populations.

Despite ongoing efforts to reduce the high prevalence of commercial tobacco use among AI/AN populations, the present study suggests that lung cancer incidence rates have largely remained stagnant among the AI/AN population. A new Government Performance and Results Act measure was established in 2006 to track tobacco-cessation service delivery among current smokers within the IHS and tribal programs.[25] Although this measure has progressively improved each year, from the baseline of 12% in 2006 to over 50% in 2016,[25] the present study suggests that expanding culturally competent tobacco control strategies for the use of commercial tobacco remains an important aspect of cancer prevention among the AI/AN population.

This study confirms persistent disparities in colorectal cancer incidence rates among the AI/AN population. Although decreasing colorectal cancer incidence rates were observed among AI/AN men in the Northern Plains and Pacific Coast regions, rates actually increased among AI/AN men in the Southwest region. There were no significant declines in colorectal cancer incidence rates among AI/AN women in regions with elevated colorectal cancer incidence, suggesting the need to increase screening for this disease. In addition, inequities in colorectal cancer risk factors could be addressed, such as higher diabetes prevalence, lower dietary intake of fruits and vegetables, and higher consumption of sugar sweetened beverages, alcohol, and tobacco products. Collaborative efforts to increase colorectal cancer screening in regions with the highest incidence of disease show promise, but alone they might not be sufficient to eliminate disparities in incidence.[26–29]

Although stomach cancer incidence rates for the overall US population are low, rates of stomach cancer among the AI/AN population are high, specifically among the Alaska Native population. The association between stomach cancer and Helicobacter pylori infection can likely account for a large portion of these increased rates of stomach cancer, specifically in Alaska, where the prevalence of infection among the AI/AN population can range from 64%–81%, and reinfection rates after treatment are as high as 16%.[30,31] Although H. pylori is an important risk factor, infection is not a sufficient cause of stomach cancer.[32] Other environmental and behavioral factors linked with the development of stomach cancer include high intake of salt, nitrites, and nitrates; family history; smoking; and obesity.[33–36] Screening and early detection of stomach cancer might be beneficial to high-risk AI/AN individuals, such as first-degree relatives of persons with stomach cancer, because survival rates after treatment of advanced-stage disease are poor.[37] Although screening high-risk populations for stomach cancer is appropriate among countries with relatively high incidence rates, screening is generally thought to be costly and unwarranted because of the low overall burden among countries with low rates of stomach cancer, such as the United States.[32] Studies have shown that data on exposure to risk factors associated with stomach cancer can aid in the identification of high-risk subgroups for more targeted screening and intervention;[38,39] these strategies might also be effective in Indian country.[37]

This study has limitations. To reduce racial misclassification of AI/AN populations, the IHS patient registration database was linked with data from the central cancer registries. However, these linkages address the racial misclassification only for individuals that have previously accessed services through the IHS; thus, AI/AN individuals who are not members of federally recognized tribes are not included. In addition, individuals living in urban, non-PRCDA areas are not represented in these data. Results based on these data might not be generalizable to all AI/AN individuals in the United States. Finally, restriction of the analyses to non-Hispanic AI/AN populations might not accurately represent all AI/AN populations. Although this exclusion reduced overall AI/AN incidence rates by less than 5%, this exclusion might disproportionally affect cancer incidence rates in certain regions. Finally, this study uses data from central cancer registries and does not consider social determinants of health that might affect cancer incidence.

The present study highlights cancers with elevated incidence among the AI/AN compared with the White populations. Elevated incidence in liver, stomach, kidney, lung, and colorectal cancers represent important health inequities between AI/AN and White populations. Areas for improvement for cancer prevention and control among the AI/AN population include efforts to promote healthy environments and address the underlying social determinants of cancer risk. Culturally informed, community-based interventions to support healthy behaviors, reduce exposure to carcinogens, promote recommended screening for cancer or its risk factors, and increase access to preventive health services could reduce these persistent disparities in cancer incidence among the AI/AN population.

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