Cohort studies of cancer mortality among American Indian (AI) adults are rare.
We explored regional differences in cancer mortality in a cohort of older AI adults.
Differences by region occurred after adjustment for potential confounders.
Leading causes of cancer mortality also differed markedly by region.
Mortality from unspecified cancer was relatively common in all regions.
Cancer mortality among American Indian (AI) people varies widely, but factors associated with cancer mortality are infrequently assessed.
Cancer deaths were identified from death certificate data for 3516 participants of the Strong Heart Study, a population-based cohort study of AI adults ages 45–74 years in Arizona, Oklahoma, and North and South Dakota. Cancer mortality was calculated by age, sex and region. Cox proportional hazards model was used to assess independent associations between baseline factors in 1989 and cancer death by 2010.
After a median follow-up of 15.3 years, the cancer death rate per 1000 person-years was 6.33 (95 % CI 5.67–7.04). Cancer mortality was highest among men in North/South Dakota (8.18; 95 % CI 6.46–10.23) and lowest among women in Arizona (4.57; 95 % CI 2.87–6.92). Factors independently associated with increased cancer mortality included age, current or former smoking, waist circumference, albuminuria, urinary cadmium, and prior cancer history. Factors associated with decreased cancer mortality included Oklahoma compared to Dakota residence, higher body mass index and total cholesterol. Sex was not associated with cancer mortality. Lung cancer was the leading cause of cancer mortality overall (1.56/1000 person-years), but no lung cancer deaths occurred among Arizona participants. Mortality from unspecified cancer was relatively high (0.48/100 person-years; 95 % CI 0.32−0.71).
Regional variation in AI cancer mortality persisted despite adjustment for individual risk factors. Mortality from unspecified cancer was high. Better understanding of regional differences in cancer mortality, and better classification of cancer deaths, will help healthcare programs address cancer in AI communities.
American Indian (AI) people experience reduced longevity [ ] and higher chronic disease mortality [ ] compared with non-Hispanic Whites (NHW) in the US. While nationwide data in the past suggested lower cancer incidence and mortality for AI people, such data were compromised by racial misclassification [ , ]. Studies that focus on areas served by indigenous or Indian Health Service (IHS) areas reduce misclassification error [ ]. For example, overall cancer mortality in a study of AI and Alaska Natives (AI/AN) in 2013–2017 was 166/100,000, higher than the All Races rate of 158/100,000 [ ]. AI/AN in another study had the highest relative risk of cancer death (1.51, 95 % CI 1.46–1.56) compared to NHW from 2006 to 2012 [ ]. Cancer mortality among AI/AN persons worsened or remained unchanged before 2010, in contrast to improved NHW rates [ , , ]. Although cancer mortality among AI/AN began to fall 0.8 % annually from 2010 to 2014, it fell faster among NHW persons (1.4 % annually) [ ].
Premature cancer mortality among AI/AN populations also worsened from 1999 to 2014–2016 [ , ]. IHS data reported that cancer, not heart disease, was the leading cause of death from 2007 to 2009 among AI persons aged 55−64 years [ ]. Premature cancer mortality was worse among AI/AN than NHW persons in other studies [ , ]. For example, cancer mortality among AI persons in South Dakota aged 40–49 was 77/100,000 from 2000 to 2010, compared to 54/100,000 among NHW [ ]. For ages 50–59, AI cancer mortality was 221/100,000 versus 176/100,000 for NHW [ ]. AI/AN cancer survival is also relatively low [ , ]. From 2006–2012, the five-year cancer survival (60.5 %) among AI/AN was lower than for other racial/ethnic groups, including NHW (68 %) [ ].
Aggregate statistics mask marked regional variations in cancer mortality. From 1999–2009, cancer mortality among AI men and women in the Northern Plains was 338.1/100,000 and 246.9/100,000, respectively, compared to 163.8/100,000 and 125.9/100,000 in the Southwest [ ]. While these differences were thought largely due to smoking [ ], few studies directly accounted for factors in assessing regional differences.
The Strong Heart Study (SHS) was designed to study cardiovascular disease (CVD) among middle- to older-aged AI participants in three geographic regions [ ]. Since 1989, SHS systematically collected data on factors common to both CVD and cancer. Previous SHS studies examined specific risk factors for cancer mortality [ ] but did not focus on regional differences. This study describes regional differences in cancer mortality in the SHS cohort, and explores whether differences persist after controlling for potential explanatory factors.