During the past 40 years, CRC incidence has increased dramatically in AN people and continues to account for the greatest cancer burden among AN people. The two-fold disparity between AN people and USWs in CRC incidence and mortality is increasing, primarily due to declining incidence rates among USWs. We were unable to detect statistical significance in rate changes over the recent 10-year period, although rates appear to have declined since the late 1990s. Survival rates for CRC have improved in the United States since 1960, more so among USWs than USBs.15
The lower survival rate among USBs has been attributed in part to later stage at diagnosis.15–17
Elevated CRC incidence in AN people does not seem to be due to a later stage at diagnosis; AN people have similar proportions of CRC diagnosed at the distant stage, as do USWs.
Chronic disease risk factor data for AN people collected in a prospective study, (Education and Research Towards Health [EARTH]) have provided some baseline information on potential levels of risk for cancer among this population. The study recruited over 3800 participants from three regions in Alaska and collected medical measurements and information on diet, lifestyle, and behavioral health, and chronic diseases. Dietary shifts away from traditional foods to a more general U.S. diet were noted. The EARTH study reported that fewer than 25% of AN participants acquired all or almost all of their food from subsistence means.18
Traditional AN diet includes wild game, marine mammals, fish, berries, and wild greens; is high in protein and fats, including omega-3 fatty acids; and lacks preservatives.18,19
Some dietary studies in other populations have indicated that a diet high in fruit and vegetable consumption may lower the risk of CRC, but results have been mixed.20–22
If such a diet is indeed beneficial, the seasonal availability of these foods in Alaska may reduce the overall protective effect. Farm-raised red meats and processed foods, associated with an increased risk of CRC, have become more available to AN people living in rural areas.23,24
Information on fruit and vegetable intake of AN people is collected in the Alaska Behavioral Risk Factor Surveillance Survey (BRFSS), a telephone survey conducted annually since 1991. In the 2009 BRFSS, 14% of AN people reported eating five or more servings of fruits and vegetables per day, compared to 25% reported by Alaska's non-native population.25
Other potential risk factors include tobacco use, diabetes, and obesity. CRC incidence has been shown to be higher among smokers.26
The BRFSS has consistently reported a relatively high proportions of smokers among AN people (2009 survey: 39% among AN people, compared to the Alaska non-native population current smoking rate of 19%).25
Type 2 diabetes has been associated with increased risk of CRC. Among AN people, the disease, once well below the rate in USWs, is increasing, particularly in the 15- to 34-year age group.27
Incidence rates of diabetes doubled from 16 per 10,000 population from 1986 through 1990 to 33 per 10,000 in the more recent period 2002 through 2006. The 2009 BRFSS data for AN people indicated that 6% of AN people surveyed reported diabetes (Alaska non-native: 6%).25
Being overweight has also been associated with an increased risk of CRC.28
The 2009 BRFSS data show that among AN people, 41% reported being overweight, with a BMI between 25 and 29.9 (Alaska non-native, 38%), and 32% met the definition of obese, with a BMI of 30 or more based on reported height and weight (Alaska non-native, 24%).25
Forty-six percent did not meet the recommendations for moderate physical activity. Diabetes coupled with the increases in body weight, shifts towards a higher fat diet and reduced levels of physical activity, as reported through the BRFSSs, are likely contributing risk factors to CRC and other chronic diseases in AN people.
Hereditary risk factors, such as familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome, may account for 5% to 10% of CRCs in the general U.S. population.4
HNPCC, a result of germ-line mutations in DNA-mismatched repair genes, does not appear to be unusually high in AN people. A review of archived CRC cancer tissue specimens indicated levels of expression of DNA-mismatched repair genes in AN people similar to those found in a study of other U.S. populations.29
Further studies of risk factors, including possible genetic factors are needed to explore possible causes of high CRC incidence rates in AN people.
Smoking cessation and CRC screening programs to address modifiable risk factors for CRC are current approaches to reducing CRC incidence and mortality. CRC control is a national priority for the National Comprehensive Cancer Control Program (NCCCP), and the resulting funding provided by the Centers for Disease Control (CDC) to states, tribes, and tribal organizations has allowed for enhanced interventions since 1998.30
Screening for CRC has been identified as a priority among tribal healthcare providers throughout Alaska. Since 1998, enhanced funding has allowed for CRC screening. The greater proportion of in situ
cancers seen in AN CRC diagnoses compared with USW proportions may be due to an increase in screening in several areas of the state as well as efforts to target first-degree relatives of individuals diagnosed with CRC.
Alaska Tribal Health System efforts have focused on addressing barriers to early detection and increasing screening opportunities for AN people, particularly in rural areas. One approach has been to provide additional itinerant colonoscopy screening clinics in conjunction with patient navigators at regional healthcare facilities not providing screening services and training for midlevel providers to perform flexible sigmoidoscopies at regional health facilities.31,32
In addition, more than 300 Community Health Aides and Practitioners working in rural Alaska communities received extensive cancer education training. A variety of culturally sensitive CRC educational materials have been made available to AN people living in communities throughout Alaska.33
BRFSS data from 2002 to 2010 indicate CRC screening (persons responding that they had a sigmoidoscopy or colonoscopy) was reported by approximately half of the individuals aged 50 years and older who responded to the surveys. The 2011 survey indicated that this proportion had increased to 65% among AN people.34
A study of CRC screening rates in American Indian/AN people who used the Indian Health Service for healthcare from 1996 through 2004 found the highest screening rates of 5 U.S. geographic areas to be among AN people.35
Recently, three Alaska regional tribal groups were awarded a CDC colorectal cancer control program (CRCCP) grant to enhance efforts to increase CRC screening through existing Breast and Cervical Cancer Program offices.36
Elevated CRC incidence rates among persons under the age of 50 are of particular interest to providers, since screening is not recommended until age 50 for those of average risk. Age-specific incidence rates for AN people are double those of USW for ages 30 to 39 (11.3 vs. 5.6/100,000) and 40 to 49 (45.1 vs. 19.8/100,000). In an effort to identify persons at increased risk, an outreach program has been developed to identify family members of CRC patients who could benefit from early or more frequent screening.
A high prevalence of Helicobacter pylori
in the AN population, often resulting in chronic gastritis, limits the use of guaiac tests to detect blood in the stool.37
In an ongoing study to determine the feasibility of using a human hemoglobin-specific stool blood assay, the fecal immunochemical test (FIT), the specificity and sensitivity of the test are compared that of the guaiac fecal occult blood test (FOBT) among study participants who undergo colonoscopy.38
The FIT test, if shown to have high test sensitivity and specificity for CRC, could greatly benefit AN people living in rural areas through early detection.
Although the rate of colon cancer in AN men may have declined since the mid-1990s, the high rate of CRC in AN people emphasizes the need for screening programs and interventions to reduce known modifiable risks. Certain behaviors that contribute to increased risk of CRC are being addressed through smoking cessation and diabetes programs; however, changing behaviors to reduce risk from excess weight, excess alcohol, physical inactivity, and diet remain the major challenges for public health intervention. Research in methods to promote healthy behaviors among AN people is greatly needed.