Abstract
Background:
American Indian and Alaska Native (AI/AN) populations have experienced regional variation and disparities in colorectal cancer incidence rates.
Methods:
We examined colorectal cancer incidence (2013–2017) and colorectal cancer incidence trends (1999–2017) among AI/AN persons. Incidence data were linked to Indian Health Service enrollment records, and analyses were restricted to Purchased/Referred Care Delivery Areas. Incidence rates of colorectal cancer among AI/AN and White persons were analyzed in six geographic regions; Hispanic persons were excluded. Incidence trends were analyzed using linear modeling.
Results:
During 2013–2017, colorectal cancer incidence was 41% higher among AI/AN than among White persons. AI/AN incidence rates per 100,000 varied regionally from 34.4 in the East to 96.1 in Alaska. Compared with White persons, AI/AN persons had higher colorectal cancer incidence rates among all age strata and were more likely to have late-stage diagnoses. Incidence rate trends indicated significant increases among both AI/AN and White persons ages <50 years and among AI/AN persons ages 50–64 years. The colorectal cancer incidence rate trend increased among AI/AN persons in the Southwest.
Conclusions:
The disparity of colorectal cancer incidence rates between AI/AN and White persons has widened since 2005–2009. AI/AN populations have higher colorectal cancer incidence compared with White populations, especially in the Alaska region.
Impact:
Our finding of increased colorectal cancer incidence disparities suggests that enhanced screening efforts and culturally appropriate clinical and public health interventions are needed among AI/AN persons overall, and especially in regions and age groups in which colorectal cancer rates are increasing.
Introduction
An estimated 1 in 23 American Indian and Alaska Native (AI/AN) persons (4.3%) may develop colorectal cancer during their lifetime, according to 2012–2016 data (1). The true incidence rate of colorectal cancer among AI/AN persons has often been underestimated because of high rates of race misclassification of AI/AN people in medical records (2), and large variation in incidence rates among AI/AN popuations by geographic area (3, 4). As a result, disparities in colorectal cancer between AI/AN and other populations are not fully understood or recognized.
By linking Indian Health Service (IHS) patient registration data with National Cancer Registry data, new databases that provide more accurate colorectal cancer incidence estimates for AI/AN persons have been created (5). When applied in a study using 2005–2009 colorectal cancer incidence data, this approach revealed that AI/AN persons had higher incidence rates than non-Hispanic White persons in every age group, and that significant variation existed among regional AI/AN rates (6). The purpose of this current study is to examine disparities in colorectal cancer incidence rates by age and stage at diagnosis, and trends over time among AI/AN populations in six regions by using race-corrected data covering the most recent years available (through 2017) in our AI/AN Incidence Analytic Database (7). By identifying the disparities in colorectal cancer incidence rates and trends among various regions, we can highlight areas that may benefit most from enhanced cancer control measures among AI/AN persons.
Materials and Methods
Population estimates
As described in a previous study, the 2010 bridged, intercensal population estimates significantly overestimated the number of AI/AN persons of Hispanic origin (8). We used these census population estimates as our denominator when calculating incidence rates. For this reason, we excluded Hispanic AI/AN from our analyses, to avoid having an inflated AI/AN population in our denominator, which would have led to an underestimation of colorectal cancer incidence rates among AI/AN persons. As a result, we limited our analyses to non-Hispanic AI/AN populations and used non-Hispanic White persons as the referent group. To be concise, non-Hispanic AI/AN and non-Hispanic White persons will be referred to as AI/AN and White persons, respectively, throughout the remainder of this article.
Incidence data
Colorectal cancer cases from 2013 to 2017 were obtained from records at cancer registries which make up the National Program of Cancer Registries (NPCR; ref. 9) at the Centers for Disease Control and Prevention and the Surveillance, Epidemiology, and End Results (SEER) program (10) at the NCI. These registries must meet data quality criteria developed for the U.S. Cancer Statistics data publication (7) in any given year and they utilize the Third Edition of the International Classification of Diseases for Oncology (ICD-O-3; ref. 11) to determine primary cancer sites.
To identify colorectal cancer cases among AI/AN persons in which a racial category had been incorrectly assigned, cancer registry records were linked with IHS patient registration data using methods that have been described in detail by Espey and colleagues (5). The SEER summary staging system was used to classify cancer stage at diagnosis: localized (tumor confined to colon or rectum); regional (tumor extension to adjacent organs or tissues and/or invasion of regional lymph nodes); distant (tumor spread to distant organs or lymph nodes); and unstaged (12).
Geographic coverage
Analyses were restricted to IHS Purchased/Referred Care Delivery Areas (PRCDA), which are U.S. counties that include all or part of a reservation, or have a common boundary with a reservation. The IHS previously referred to these counties as Contract Health Service Delivery Area (CHSDA) counties (6). PRCDA residence is used by the IHS to determine eligibility for health care services that are not directly available through IHS. Linkage studies have indicated that there is less racial misclassification of AI/AN persons in PRCDA counties (2, 13). PRCDA counties also have higher proportions of AI/AN populations, in relation to the total population, than non-PRCDA counties. Although the 651 PRCDA counties represent only 20.7% of the 3,141 counties in the United States, 53.3% of all AI/AN persons resided in those PRCDA-designated counties from 2013 to 2017. By restricting analyses to the PRCDA counties, we can improve the accuracy of colorectal cancer incidence rates among AI/AN populations.
Analyses were completed for all regions combined and for six individual IHS regions, as described by Espey and colleagues (13). By IHS region, the percentages of AI/AN persons living in PRCDA counties during this time were: Alaska (100%); Pacific Coast (60.3%); Southwest (83.9%); Northern Plains (54.3%); Southern Plains (56.7%); and East (16.8%) (7). Identical or similar regional configurations have been used for other health-related publications focusing on AI/AN populations (14–16).
Statistical methods
All rates were expressed as number of cases per 100,000 population and directly age adjusted to the 2000 U.S. standard population (Census P25–1130) by using SEER*Stat software (17). Comparisons with published incidence rates using other population standards could be biased because of differing population age distribution adjustments.
From these age-adjusted incidence rates, standardized rate ratios (RR) were calculated for AI/AN compared with White persons. Confidence intervals for age-adjusted rates and RR were calculated by using SEER*Stat 8.0.2, based on methods described by Tiwari and colleagues (18). Changes in annual age-adjusted incidence rates over time, including the average annual percent change (AAPC), were assessed with Joinpoint software (19). We used AAPC to report trends over the entire period since the number of cancers in AI/AN populations are more sparse and may not allow for stable estimates of annual percent change joinpoints. Statistical significance was set at P < 0.05.
Results
Incidence
During 2013–2017, a total of 3,742 AI/AN persons and 125,115 White persons were diagnosed with colorectal cancer (Table 1). The colorectal cancer incidence rate for AI/AN persons from all PRCDA counties combined was 41% higher (P < 0.05) than the comparable rate for White persons (51.2 vs. 36.3 per 100,000 population, respectively). Differences in rates and RRs by race were similar among both males and females.
Table 1.
Colorectal cancer incidence rates by IHS region and sex for AI/ANa,b and Whitea persons in PRCDA counties, United States, 2013–2017.
| AI/AN | White | AI/AN:White | |||||
|---|---|---|---|---|---|---|---|
| IHS region | Cases | Ratec | Cases | Ratec | RRd | CI | |
| Northern Plains | Both sexes | 687 | 63.7 | 19,498 | 37.3 | 1.71e | 1.57–1.85 |
| Male | 365 | 75.7 | 10,286 | 42.0 | 1.80e | 1.60–2.02 | |
| Female | 322 | 54.5 | 9,212 | 33.1 | 1.65e | 1.46–1.85 | |
| Alaska | Both sexes | 419 | 96.1 | 890 | 35.9 | 2.68e | 2.36–3.03 |
| Male | 197 | 93.4 | 505 | 38.4 | 2.43e | 2.02–2.91 | |
| Female | 222 | 98.0 | 385 | 33.0 | 2.97e | 2.48–3.53 | |
| Southern Plains | Both sexes | 1,016 | 65.3 | 7,814 | 39.9 | 1.64e | 1.53–1.75 |
| Male | 546 | 77.1 | 4,180 | 46.0 | 1.68e | 1.52–1.84 | |
| Female | 470 | 55.6 | 3,634 | 34.6 | 1.61e | 1.45–1.78 | |
| Pacific Coast | Both sexes | 626 | 43.4 | 37,245 | 35.6 | 1.22e | 1.12–1.32 |
| Male | 300 | 44.8 | 19,467 | 39.7 | 1.13 | 0.99–1.28 | |
| Female | 326 | 42.3 | 17,778 | 32.0 | 1.32e | 1.18–1.48 | |
| East | Both sexes | 214 | 34.4 | 42,722 | 37.3 | 0.92 | 0.80–1.06 |
| Male | 97 | 34.1 | 22,248 | 42.5 | 0.80e | 0.64–0.99 | |
| Female | 117 | 35.4 | 20,474 | 32.8 | 1.08 | 0.89–1.30 | |
| Southwest | Both sexes | 780 | 36.0 | 16,946 | 33.4 | 1.08e | 1.00–1.16 |
| Male | 418 | 43.7 | 9,129 | 37.4 | 1.17e | 1.05–1.30 | |
| Female | 362 | 29.9 | 7,817 | 29.6 | 1.01 | 0.90–1.12 | |
| All regions | Both sexes | 3,742 | 51.2 | 125,115 | 36.3 | 1.41e | 1.36–1.49 |
| Male | 1,923 | 57.9 | 65,815 | 41.0 | 1.41e | 1.35–1.48 | |
| Female | 1,819 | 45.8 | 59,300 | 32.2 | 1.42e | 1.35–1.49 | |
Note: The percentage of the AI/AN population living in a PRCDA-designated county from 2013–2017 was 53.3% for the United States; by IHS region, these percentages were: Alaska = 100%; Pacific Coast = 60.3%; Southwest = 83.9%; Northern Plains = 54.3%; Southern Plains = 56.7%; and East = 16.8%.
Abbreviations: AI/AN, American Indian/Alaska Native; CI, confidence interval; IHS, Indian Health Service; PRCDA, Purchased/Referred Care Delivery Area; RR, rate ratio.
Analyses are limited to persons of non-Hispanic origin.
AI/AN race for incidence data is reported by NPCR and SEER registries or through linkage with the IHS patient registration database.
Rates are per 100,000 persons and are age adjusted to the 2000 U.S. standard population (19 age groups—Census P25–1130).
Rate ratios are calculated in SEER*Stat prior to rounding of rates and may not equal rate ratios calculated from rates presented in table.
Indicates rate ratio is statistically significant (P < 0.05).
Source: National Program of Cancer Registries and Surveillance, Epidemiology, and End Results SEER*Stat Database: U.S. Cancer Statistics American Indian and Alaska Native Incidence Analytic Database - 1998–2017. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Released June 2020, based on the 2019 submission.
IHS regions are defined as follows: Alaska*; Northern Plains (IL, IN*, IA*, MI*, MN*, MT*, NE*, ND*, SD*, WI*, WY*); Southern Plains (OK*, KS*, TX*); Southwest (AZ*, CO*, NV*, NM*, UT*); Pacific Coast (CA*, ID*, OR*, WA*, HI); East (AL*, AR, CT*, DE, FL*, GA, KY, LA*, ME*, MD, MA*, MS*, MO, NH, NJ, NY*, NC*, OH, PA*, RI*, SC*, TN, VT, VA*, WV, DC); * identifies states with at least one county designated as PRCDA.
Colorectal cancer incidence among AI/AN persons varied regionally (Table 1). Colorectal cancer incidence rates for both sexes combined ranged widely among AI/AN persons (34.4 in the East to 96.1 in Alaska), whereas less regional variation was seen in rates among White persons (33.4 in the Southwest to 39.9 in Southern Plains). Regional rates among AI/AN persons were significantly higher (P < 0.05) than among White persons in five regions: Alaska (RR = 2.68), Northern Plains (RR = 1.71), Southern Plains (RR = 1.64), Pacific Coast (RR = 1.22), and Southwest (RR = 1.08). Rates were similar in the East region. Among females, the AI/AN rates were higher than White rates in all regions except the Southwest and East, where rates were similar. Among males, the incidence rates for AI/AN persons were significantly higher than White rates in every region except the Pacific Coast region (no significant rate difference), and the East region, where the rate among AI/AN males was significantly lower than the rate among White males (RR = 0.80).
Age at diagnosis
When analyzing data from all regions combined by age categories, AI/AN populations had an increased risk of colorectal cancer compared with White persons in every age category: 43% higher among AI/AN persons ages younger than 50 years; 56% higher among those ages 50–64 years; 45% higher among those ages 65–74 years; 29% higher among those ages 75–84 years; and 20% higher among those ages 85 years or older. (all P < 0.05; see Table 2).
Table 2.
Colorectal cancer incidence by IHS region and age at diagnosis for AI/ANa,b and Whitea residents of PRCDA counties, both sexes combined, United States, 2013–2017.
| AI/AN | White | AI/AN:White Rate Ratio | |||||||
|---|---|---|---|---|---|---|---|---|---|
| IHS region | Age at diagnosis | N | % | Ratec | N | % | Ratec | RRd | CI |
| Northern Plains | <50 years | 114 | 16.60 | 13.9 | 1,899 | 9.70 | 8.2 | 1.69e | 1.38–2.05 |
| 50–64 years | 286 | 41.60 | 124.8 | 5,575 | 28.60 | 62.5 | 2.00e | 1.77–2.25 | |
| 65–74 years | 153 | 22.30 | 207.5 | 4,880 | 25.00 | 124.7 | 1.66e | 1.40–1.96 | |
| 75–84 years | 112 | 16.30 | 377.3 | 4,524 | 23.20 | 215.3 | 1.75e | 1.44–2.11 | |
| 85+ years | 22 | 3.20 | 277.2 | 2,620 | 13.40 | 265.6 | 1.04 | 0.65–1.58 | |
| Alaska | <50 years | 70 | 16.70 | 21.5 | 112 | 12.60 | 7.6 | 2.85e | 2.07–3.87 |
| 50–64 years | 158 | 37.70 | 168.9 | 348 | 39.10 | 63.6 | 2.66e | 2.19–3.22 | |
| 65–74 years | 97 | 23.20 | 327.1 | 250 | 28.10 | 132.1 | 2.48e | 1.93–3.16 | |
| 75–84 years | 75 | 17.90 | 573.2 | 136 | 15.30 | 204.5 | 2.80e | 2.09–3.74 | |
| 85+ years | 19 | 4.50 | 507.9 | 44 | 4.90 | 190.7 | 2.66e | 1.47–4.66 | |
| Southern Plains | <50 years | 155 | 15.30 | 14.2 | 771 | 9.9 | 8.9 | 1.60e | 1.34–1.90 |
| 50–64 years | 395 | 38.90 | 128.6 | 2,316 | 29.60 | 72.0 | 1.79e | 1.60–1.99 | |
| 65–74 years | 256 | 25.20 | 231.3 | 2,284 | 29.20 | 151.7 | 1.52e | 1.33–1.74 | |
| 75–84 years | 147 | 14.50 | 300.2 | 1,680 | 21.50 | 203.7 | 1.47e | 1.24–1.75 | |
| 85+ years | 63 | 6.20 | 451.6 | 763 | 9.80 | 225.4 | 2.00e | 1.52–2.59 | |
| Pacific Coast | <50 years | 90 | 14.40 | 9.7 | 3,557 | 9.60 | 7.8 | 1.24 | 0.99–1.53 |
| 50–64 years | 242 | 38.70 | 80.6 | 11,252 | 30.20 | 64.4 | 1.25e | 1.10–1.42 | |
| 65–74 years | 161 | 25.70 | 153.3 | 9,509 | 25.50 | 115.0 | 1.33e | 1.13–1.56 | |
| 75–84 years | 92 | 14.70 | 212.8 | 8,054 | 21.60 | 196.4 | 1.08 | 0.87–1.33 | |
| 85+ years | 41 | 6.50 | 296.8 | 4,873 | 13.10 | 252.9 | 1.17 | 0.84–1.59 | |
| East | <50 years | 32 | 15.00 | 8.7 | 4,145 | 9.70 | 8.5 | 1.02 | 0.70–1.45 |
| 50–64 years | 93 | 43.50 | 78.4 | 12,364 | 28.90 | 65.9 | 1.19 | 0.96–1.46 | |
| 65–74 years | 52 | 24.30 | 116.0 | 10,961 | 25.70 | 125.0 | 0.93 | 0.69–1.22 | |
| 75–84 years | 23 | 10.70 | 123.0 | 9,506 | 22.30 | 202.9 | 0.61e | 0.38–0.91 | |
| 85+ years | 14 | 6.50 | 206.2 | 5,746 | 13.40 | 252.0 | 0.82 | 0.45–1.37 | |
| Southwest | <50 years | 130 | 16.70 | 8.3 | 1,438 | 8.50 | 7.1 | 1.16 | 0.96–1.39 |
| 50–64 years | 311 | 39.90 | 74.3 | 4,941 | 29.20 | 63.6 | 1.17e | 1.04–1.31 | |
| 65–74 years | 175 | 22.40 | 120.3 | 4,760 | 28.10 | 110.4 | 1.09 | 0.93–1.27 | |
| 75–84 years | 119 | 15.30 | 173.7 | 3,953 | 23.30 | 178.0 | 0.98 | 0.81–1.17 | |
| 85+ years | 45 | 5.80 | 202.9 | 1,854 | 10.90 | 218.1 | 0.93 | 0.68–1.25 | |
| All regions | <50 years | 591 | 15.80 | 11.6 | 11,922 | 9.50 | 8.1 | 1.43e | 1.31–1.55 |
| 50–64 years | 1,485 | 39.70 | 101.2 | 36,796 | 29.40 | 64.9 | 1.56e | 1.48–1.64 | |
| 65–74 years | 894 | 23.90 | 175.6 | 32,644 | 26.10 | 121.1 | 1.45e | 1.35–1.55 | |
| 75–84 years | 568 | 15.20 | 255.8 | 27,853 | 22.30 | 198.9 | 1.29e | 1.18–1.40 | |
| 85+ years | 204 | 5.50 | 298.2 | 15,900 | 12.70 | 248.3 | 1.20e | 1.04–1.38 | |
Note: The percentage of the AI/AN population living in a PRCDA-designated county from 2013–2017 was 53.3% for the United States; by IHS region, these percentages were: Alaska = 100%; Pacific Coast = 60.3%; Southwest = 83.9%; Northern Plains = 54.3%; Southern Plains = 56.7%; and East = 16.8%.
Abbreviations: AI/AN, American Indian/Alaska Native; CI, confidence interval; IHS, Indian Health Service; N, number; RR, rate ratio.
Analyses are limited to persons of non-Hispanic origin.
AI/AN race is reported by NPCR and SEER registries or through linkage with the IHS patient registration database.
Rates are per 100,000 persons and are age adjusted to the 2000 U.S. standard population (19 age groups—Census P25–1130).
Rate ratios are calculated in SEER*Stat prior to rounding of rates and may not equal rate ratios calculated from rates presented in table.
Indicates rate ratio is statistically significant (P < 0.05).
Source: National Program of Cancer Registries and Surveillance, Epidemiology, and End Results SEER*Stat Database: U.S. Cancer Statistics American Indian and Alaska Native Incidence Analytic Database - 1998–2017. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Released June 2020, based on the 2019 submission.
IHS regions are defined as follows: Alaska*; Northern Plains (IL, IN*, IA*, MI*, MN*, MT*, NE*, ND*, SD*, WI*, WY*); Southern Plains (OK*, KS*, TX*); Southwest (AZ*, CO*, NV*, NM*, UT*); Pacific Coast (CA*, ID*, OR*, WA*, HI); East (AL*, AR, CT*, DE, FL*, GA, KY, LA*, ME*, MD, MA*, MS*, MO, NH, NJ, NY*, NC*, OH, PA*, RI*, SC*, TN, VT, VA*, WV, DC); * identifies states with at least one county designated as PRCDA.
Regionally, AI/AN men and women combined in Alaska and the Southern Plains had higher colorectal cancer incidence rates than White persons in every age strata. In the Northern Plains region, there were significantly higher rates among AI/AN persons in every age group, except among persons ages 85 years or older. In the Pacific Coast region, the colorectal cancer incidence rate was significantly higher among AI/AN persons ages 50–74 years. In the Southwest region, the rate was higher only among AI/AN persons ages 50–64 years, with no significant rate differences among other age categories. In the East region, incidence rates were also similar between AI/AN and White persons among most age categories, except for a significantly lower incidence rate among AI/AN persons ages 75–84 years.
The proportion of colorectal cancer cases diagnosed among AI/AN persons ages younger than 50 years was larger than it was among White persons (15.8% and 9.5%, respectively), whereas 63.6% of all cases among AI/AN persons and 55.5% of all cases among White persons were ages 50–74 years at time of diagnosis, and the remaining 20.7% of cases among AI/AN persons were ages 75 years or older compared with 35% of cases among White persons (Table 2).
Stage at diagnosis
Among AI/AN persons, the rate of early-stage, localized colorectal cancer was 24% higher, regional-stage colorectal cancer was 43% higher, and distant-stage colorectal cancer was 51% higher, compared with rates among White persons at each stage of diagnosis (Table 3). In the Northern Plains, Alaska, and Southern Plains regions, rates were consistently elevated among AI/AN persons at all stages of diagnosis compared with White persons, except unstaged in the Alaska region.
Table 3.
Colorectal cancer incidence by IHS region and stage at diagnosis for AI/ANa,b and Whitea residents of PRCDA counties, both sexes combined, United States, 2013–2017.
| AI/AN | White | AI/AN:White Rate Ratio | |||||||
|---|---|---|---|---|---|---|---|---|---|
| IHS region | Stage at diagnosis | N | % | Ratec | N | % | Ratec | RRd | CI |
| Northern Plains | Localized | 223 | 32.5 | 19.6 | 7,081 | 36.3 | 13.5 | 1.45e | 1.25–1.67 |
| Regional | 267 | 38.9 | 25.9 | 7,138 | 36.6 | 13.7 | 1.89e | 1.65–2.15 | |
| Distant | 161 | 23.4 | 14.5 | 3,967 | 20.3 | 7.7 | 1.88e | 1.58–2.22 | |
| Unstaged | 36 | 5.2 | 3.7 | 1,312 | 6.7 | 2.4 | 1.57e | 1.07–2.22 | |
| Alaska | Localized | 165 | 39.4 | 35.3 | 317 | 35.6 | 12.3 | 2.86e | 2.33–3.50 |
| Regional | 138 | 32.9 | 34.1 | 298 | 33.5 | 11.9 | 2.86e | 2.29–3.56 | |
| Distant | 101 | 24.1 | 22.9 | 206 | 23.1 | 8.4 | 2.72e | 2.09–3.51 | |
| Unstaged | 15 | 3.6 | 3.8 | 69 | 7.8 | 3.2 | 1.20 | 0.61–2.14 | |
| Southern Plains | Localized | 299 | 29.4 | 19.3 | 2,765 | 35.4 | 14.0 | 1.38e | 1.21–1.56 |
| Regional | 333 | 32.8 | 21.4 | 2,546 | 32.6 | 13.0 | 1.64e | 1.45–1.85 | |
| Distant | 230 | 22.6 | 14.5 | 1,616 | 20.7 | 8.4 | 1.74e | 1.50–2.01 | |
| Unstaged | 154 | 15.2 | 10.1 | 887 | 11.4 | 4.5 | 2.26e | 1.88–2.70 | |
| Pacific Coast | Localized | 216 | 34.5 | 14.8 | 13,459 | 36.1 | 12.8 | 1.15 | 0.99–1.33 |
| Regional | 236 | 37.7 | 16.3 | 13,478 | 36.2 | 13.0 | 1.26e | 1.09–1.44 | |
| Distant | 134 | 21.4 | 9.1 | 7,680 | 20.3 | 7.4 | 1.22e | 1.01–1.46 | |
| Unstaged | 40 | 6.4 | 3.2 | 2,628 | 7.1 | 2.4 | 1.32 | 0.92–1.82 | |
| East | Localized | 71 | 33.2 | 11.0 | 16,306 | 38.2 | 14.2 | 0.78e | 0.60–0.99 |
| Regional | 81 | 37.9 | 13.4 | 14,776 | 34.6 | 12.9 | 1.04 | 0.82–1.30 | |
| Distant | 51 | 23.8 | 7.8 | 8,743 | 20.5 | 7.7 | 1.01 | 0.75–1.35 | |
| Unstaged | 11 | 5.1 | 2.1 | 2,897 | 6.8 | 2.4 | 0.89 | 0.43–1.61 | |
| Southwest | Localized | 271 | 34.7 | 12.0 | 6,025 | 35.6 | 11.7 | 1.03 | 0.90–1.16 |
| Regional | 256 | 32.8 | 11.8 | 5,492 | 32.4 | 10.9 | 1.09 | 0.95–1.24 | |
| Distant | 162 | 20.8 | 7.7 | 3,377 | 19.9 | 6.8 | 1.14 | 0.96–1.34 | |
| Unstaged | 91 | 11.7 | 4.4 | 2,052 | 12.2 | 4.0 | 1.12 | 0.89–1.39 | |
| All regions | Localized | 1,245 | 33.3 | 16.6 | 45,953 | 36.7 | 13.3 | 1.24e | 1.17–1.32 |
| Regional | 1,311 | 35.0 | 18.2 | 43,728 | 35.0 | 12.8 | 1.43e | 1.35–1.51 | |
| Distant | 839 | 22.4 | 11.4 | 25,589 | 20.5 | 7.5 | 1.51e | 1.41–1.62 | |
| Unstaged | 347 | 9.3 | 5.1 | 9,845 | 7.9 | 2.7 | 1.85e | 1.65–2.07 | |
Note: The percentage of the AI/AN population living in a PRCDA-designated county from 2013–2017 was 53.3% for the United States; by IHS region, these percentages were: Alaska = 100%; Pacific Coast = 60.3%; Southwest = 83.9%; Northern Plains = 54.3%; Southern Plains = 56.7%; and East = 16.8%.
Abbreviations: AI/AN, American Indian/Alaska Native; CI, confidence interval; IHS, Indian Health Service; N, number; PRCDA, Purchased/Referred Care Delivery Area; RR, rate ratio.
Analyses are limited to persons of non-Hispanic origin.
AI/AN race is reported by NPCR and SEER registries or through linkage with the IHS patient registration database.
Rates are per 100,000 persons and are age adjusted to the 2000 U.S. standard population (19 age groups—Census P25–1130).
Rate ratios are calculated in SEER*Stat prior to rounding of rates and may not equal rate ratios calculated from rates presented in table.
Indicates rate ratio is statistically significant (P < 0.05).
Source: National Program of Cancer Registries and Surveillance, Epidemiology, and End Results SEER*Stat Database: U.S. Cancer Statistics American Indian and Alaska Native Incidence Analytic Database - 1998–2017. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Released June 2020, based on the 2019 submission.
IHS regions are defined as follows: Alaska*; Northern Plains (IL, IN*, IA*, MI*, MN*, MT*, NE*, ND*, SD*, WI*, WY*); Southern Plains (OK*, KS*, TX*); Southwest (AZ*, CO*, NV*, NM*, UT*); Pacific Coast (CA*, ID*, OR*, WA*, HI); East (AL*, AR, CT*, DE, FL*, GA, KY, LA*, ME*, MD, MA*, MS*, MO, NH, NJ, NY*, NC*, OH, PA*, RI*, SC*, TN, VT, VA*, WV, DC); * identifies states with at least one county designated as PRCDA.
For all AI/AN combined, 33.3% were diagnosed at a localized stage (regions ranged from 29.4% in the Southern Plains to 39.4% in Alaska), compared with 36.7% of all cases among White persons (regions ranged from 35.4% in Southern Plains to 38.2% in the East; Table 3). The proportion of cases diagnosed at a distant stage was higher among AI/AN persons than White persons (22.4% vs. 20.5%, respectively).
Trends
We assessed colorectal cancer incidence trends among AI/AN and White persons in PRCDA counties from 1999 to 2017, by age groups, and reported the AAPC in the age-adjusted rates (Table 4). For AI/AN persons of all ages in all regions combined, the overall AAPC in the colorectal cancer incidence rate was −0.5%, compared with a steeper decline of −2.4% AAPC among White persons. There was an increasing trend in colorectal cancer incidence rates among AI/AN persons ages younger than 50 years (AAPC = +3.7%) and those ages 50–64 years (AAPC = +1.1%). There was a decreasing trend among AI/AN persons ages 65 years or older. Among White persons, colorectal cancer incidence rates increased only among those ages younger than 50 years (AAPC = +2.5%) and decreased among those ages 50 years or older.
Table 4.
Incidence rate trends (1999–2017) for colorectal cancer with joinpointa analyses for AI/ANb,c persons compared to Whiteb persons in PRCDA counties, both sexes combined, United States.
| AAPCd | ||||||
|---|---|---|---|---|---|---|
| IHS region | Race | <50 years | 50–64 | 65–74 | 75+ years | All ages |
| Northern Plains | White | +3.0e | −1.4e | −4.2e | −3.3e | −2.3e |
| AI/AN | +3.6e | +0.6 | −3.8e | −2.4e | −1.2e | |
| Alaska | White | +3.5e | −0.1 | −4.5e | −4.8e | −2.8e |
| AI/AN | +3.7e | −1.4 | −2.4e | −1.3 | −1.1e | |
| Southern Plains | White | +2.3e | −0.9e | −2.5e | −3.4e | −1.5e |
| AI/AN | +2.8e | +1.2e | −1.9e | −2.2e | −0.6 | |
| Pacific Coast | White | +2.9e | −0.8e | −4.2e | −3.6e | −2.4e |
| AI/AN | +4.5e | +0.4 | −2.8e | −4.6e | −1.3e | |
| East | White | No value | −2.0e | −4.2e | −4.2e | −2.8e |
| AI/AN | No value | +3.1 | −5.1e | −3.8e | −0.9 | |
| Southwest | White | +2.5e | −0.7e | −3.9e | −3.7e | −2.3e |
| AI/AN | +3.4e | +2.4e | +1.8 | +1.2 | +2.9e | |
| All regions | White | +2.5e | −1.3e | −4.1e | −3.8e | −2.4e |
| AI/AN | +3.7e | +1.1e | −2.1e | −2.0e | −0.5e | |
Note: The percentage of the AI/AN population living in a PRCDA-designated county from 2013–2017 was 53.3% for the United States; by IHS region, these percentages were: Alaska = 100%; Pacific Coast = 60.3%; Southwest = 83.9%; Northern Plains = 54.3%; Southern Plains = 56.7%; and East = 16.8%.
Abbreviations: AI/AN, American Indian/Alaska Native; AAPC, average annual percent change; IHS, Indian Health Service; PRCDA, Purchased/Referred Care Delivery Area.
Joinpoint analyses are based on rates per 100,000 persons and are age adjusted to the 2000 U.S. standard population (11 age groups, Census P25–1130).
Analyses are limited to persons of non-Hispanic origin.
AI/AN race is reported by NPCR and SEER registries or through linkage with the IHS patient registration database.
AAPC is based on rates that were age adjusted to the 2000 U.S. standard population (11 age groups—Census P25–1130).
Indicates AAPC is statistically significantly different from zero (two-sided P < 0.05).
Source: National Program of Cancer Registries and Surveillance, Epidemiology, and End Results SEER*Stat Database: U.S. Cancer Statistics American Indian and Alaska Native Incidence Analytic Database - 1998–2017. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Released June 2020, based on the 2019 submission.
IHS regions are defined as follows: Alaska*; Northern Plains (IL, IN*, IA*, MI*, MN*, MT*, NE*, ND*, SD*, WI*, WY*); Southern Plains (OK*, KS*, TX*); Southwest (AZ*, CO*, NV*, NM*, UT*); Pacific Coast (CA*, ID*, OR*, WA*, HI); East (AL*, AR, CT*, DE, FL*, GA, KY, LA*, ME*, MD, MA*, MS*, MO, NH, NJ, NY*, NC*, OH, PA*, RI*, SC*, TN, VT, VA*, WV, DC); * identifies states with at least one county designated as PRCDA.
Colorectal cancer incidence rate increased among AI/AN and White persons ages younger than 50 years in every region except the East, where data were not available (Table 4). The Southern Plains and the Southwest showed increasing rate trends among AI/AN persons ages 50–64 years—no other region showed a significant rate trend change among AI/AN persons in this age group. Among White persons, there was a decreasing trend in colorectal cancer rates for those ages 50–64 years in every region except Alaska. There was a decreasing trend in colorectal cancer incidence rates among AI/AN persons ages 65–74 years and 75 years or older in all regions except the Southwest. Among White persons, there was a decreasing trend in every region for those ages 65 years or older. For all ages combined, the Southwest was the only region with an increasing trend in colorectal cancer incidence rates among AI/AN persons (2.9% average annual increase from 1999 to 2017), whereas every region had a decreasing colorectal cancer incidence trend among White persons from 1999 to 2017 (Table 4).
Discussion
Among AI/AN persons, the highest regional colorectal cancer incidence rates were found in Alaska, followed by Southern Plains and Northern Plains regions. There was a nearly 3-fold difference in rates between AI/AN persons in the Alaska region and AI/AN persons in the region with the lowest rate (East). Several risk factors that influence colorectal cancer include inadequate physical activity, commercial tobacco use, alcoholic beverage consumption, dietary patterns that include eating red and processed meat, and having excess body weight (20). The wide variation in regional AI/AN colorectal cancer rates may be influenced by differences in the prevalence of these risk factors, or other environmental factors, among AI/AN populations, which has been noted in prior research (21, 22). These regional differences in colorectal cancer rates and risk factor prevalence among AI/AN populations suggest the need for further research to identify clinical and community-based interventions that can be adapted to the unique context of AI/AN populations to reduce the prevalence of colorectal cancer risk factors among AIAN persons.
From 2013 to 2017, colorectal cancer incidence rates were significantly higher among AI/AN than White persons in five of six regions. In a previous study, which examined incidence from 2005 to 2009 (using the same methods as our current study), the colorectal cancer incidence rate among AI/AN persons in all CHSDA (now called PRCDA) counties combined was 21% higher than the rate among White persons in those same counties (6). In a study by May and colleagues, the disparity in colorectal cancer incidence between White and Black persons was at its peak in 2004, when the incidence rate for Black persons was 21% higher than the rate for White persons, followed by a decreased disparity in incidence from 2004 to 2012 (23). The disparity in colorectal cancer incidence rates widened in our current study; AI/AN persons from all regions combined experienced a 41% higher incidence rate compared with White persons. Our trend data revealed that although colorectal cancer incidence rates were decreasing in most regions among both AI/AN and White populations, they decreased at a slower pace among AI/AN populations compared with the steeper decrease among White populations. This resulted in increased RRs between AI/AN and White persons in the Alaska, Southern Plains, Northern Plains, and Pacific Coast regions (Table 1), compared with RRs found during the previous study period (6).
Trend analyses also showed that the rate of colorectal cancer incidence among AI/AN persons in one region, the Southwest, increased significantly, while decreasing among White persons in that region. The Southwest was the only region that experienced an increasing trend in colorectal cancer incidence rate among either AIAN or White populations, with a 2.9% average annual percent increase in colorectal cancer incidence rate from 1999 to 2017. As a result of this trend, the colorectal cancer incidence rate among Southwest AI/AN persons, which was 21% lower than that of White persons during the previous study period (2005–2009), was 8% higher than the rate among White persons during 2013–2017. One contributor to the observed trend may be a lack of access to health care among AI/AN persons in the region. From 2000 to 2010, the Southwest had the lowest percentage of any region of AI/AN persons to report having health care coverage or a personal health care provider (68.8% and 61.3%, respectively; ref. 21). Providing AI/AN persons with equal access to health care, especially cancer screening, could help reduce the colorectal cancer incidence disparity between AI/AN and White persons in all regions.
In a study by Lansdorp-Vogelaar and colleagues, differences in colorectal cancer screening accounted for 42% of the disparity in colorectal cancer incidence between their study populations (24). Lower colorectal cancer screening prevalence among AI/AN persons may account for some of the colorectal cancer incidence disparity we observed between AI/AN and White populations. AI/AN persons often live in areas that have large gaps in the availability of, the use of, and the distance to health care providers, compared with other areas (25). Our results showed that a substantial proportion of colorectal cancer cases are occurring among AI/AN persons ages 50–74 years, which is similar to other subpopulations. Data from the 2015 National Health Interview Survey, which uses self-reported data, showed 63.7% of White persons were up-to-date with colorectal cancer screening compared with 48.4% of AI/AN persons (26). Screening estimates from the IHS, which utilize administrative data, are even lower. In 2019, only 31.5% of AI/AN men and women served by the IHS were up-to-date with colorectal cancer screening (27). The screening prevalence in the IHS administrative areas that make up the Southwest region (which has an increasing colorectal cancer incidence rate trend), ranged from 25.9% in the Phoenix Area to 35.1% in the Navajo Area in 2019. Continued efforts are needed to improve colorectal cancer screening uptake among AI/AN populations.
Past studies have indicated that AI/AN persons are often diagnosed with colorectal cancer at younger ages than White persons (28, 29). In general, the colorectal cancer incidence rate is low among persons ages younger than 50 years, but has been increasing (30, 31). Our study results corroborate this, revealing an increasing trend in rates among both AI/AN and White persons ages younger than 50 years, with a higher average annual percent increase among AI/AN than White persons (+3.7 vs. +2.5, respectively). Overall, during 2013–2017, more than 1 in 7 colorectal cancer cases among AI/AN persons were diagnosed among persons ages younger than 50 years, compared with less than 1 in 10 cases among White persons. The U.S. Preventive Services Task Force has revised its colorectal cancer screening recommendation to state that average-risk individuals should begin screening at 45 years of age (32). Health care facilities can inform their average-risk patients and providers of the importance of initiating screening at the recommended age. This is especially true for AI/AN persons, because our results show that colorectal cancer incidence has increased among persons ages younger than 50 years and among adults ages 50–64 years in many regions.
Initiation of colorectal cancer screening at the recommended age also increases the chances of detecting cancer at an early stage. The 5-year survival estimate for persons diagnosed with colorectal cancer at an early stage is over 90%, but falls sharply to 14% for those diagnosed with distant-stage disease (33). In our study, Alaska was the region with the highest proportion of AI/AN persons diagnosed in the localized stage of disease (39.4%), which might have been influenced by the decision of the Alaska Native Medical Center in 2013 to begin screening average risk individuals at age 40 (34, 35).
Our study has some limitations. The percentage of AI/AN persons in the United States living in the PRCDA-designated counties used in our analyzes was 53.3%, and the percentage varied by region, ranging from 100% residing in PRCDA counties in Alaska to 16.8% in the East region. Our results cannot be generalized to the entire AI/AN population. The IHS provides care to 2.6 million of the estimated 5.2 million AI/AN persons in the United States (36), and our study approach could not correct racial misclassification for AI/AN persons in PRCDA counties who did not receive care through IHS. This includes AI/AN persons from nonfederally recognized tribes and persons who did not have direct tribal ties, or lived long distances from IHS and tribal health facilities. It is possible that our reported colorectal cancer incidence rates among AI/AN persons were underestimated. Our analyses were also limited to non-Hispanic AI/AN and White persons, which could have also impacted cancer incidence rates, particularly in regions that may have higher percentages of Hispanic persons.
We found that the disparity in colorectal cancer incidence rates between AI/AN and White populations increased during the past decade, as rates among AI/AN populations declined at a slower pace than rates among White populations. Regional variation in colorectal cancer rates persists among AI/AN populations, with the highest rate in Alaska, and with an increasing rate in the Southwest region. Future emphasis should be placed on determining which risk factors contribute the most to the regional rate differences and addressing those factors, especially among AI/AN persons in the Southwest where the colorectal cancer incidence rate is increasing. With increased colorectal cancer rates among persons ages younger than 50 years, more urgency is needed for increased colorectal cancer screening, and initiation of screening at the recommended age. All of these actions can help reduce the disparity of colorectal cancer incidence experienced among AI/AN populations in the United States.
Footnotes
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Publisher's Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
Authors’ Disclosures
No disclosures were reported.
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