Previous studies have found that the urban American Indian and Alaskan Native (AIAN) community has higher cancer incidence than other racial or ethnic groups.
But the data used in these analyses may have been skewed. This is because they came from the Indian Health Service (IHS), which is an agency within the Department of Health and Human Services. It is responsible for providing health services to AIANs.
IHS facilities are only found near reservation lands, and an estimated 80 percent of AIANs are not eligible to use these services. For this reason, previous findings may not be reliable as they were not taken from a representative sample.
Other studies have found that, while cancer mortality has gradually decreased in some ethnic groups — including non-Hispanic white (NHW) and black people — mortality rates have either remained stagnant or become worse in AIAN populations.
Muddying the water further, significant regional differences have been shown in cancer rates and cancer mortality rates across AIAN populations.
AIAN communities and cancer mortality
The new study examined AIANs within an urban setting, taking data from people enrolled at Kaiser Permanente Northern California (KPNC), a healthcare system that covers roughly one third of the residents in the Bay Area and Central Valley.
In total, there were data from 582 AIANs. This information was then compared with data from more than 80,000 NHW people.
The study was led by Marc A. Emerson, from the Department of Epidemiology at the University of North Carolina at Chapel Hill, and Laurel A. Habel, Ph.D., from KPNC's Division of Research. Their findings are published this month in the journal Cancer Research.
From January 1997 to December 2015, diagnoses of primary invasive colorectal, breast, lung, and prostate cancer were collated. Because all participants were involved in the same comprehensive health plan, their access to treatment and preventative programs was approximately equal.
Despite this theoretical equality, AIANs were found to have a higher comorbidity burden when compared with NHWs.
"The AIAN population has a unique history of social, environmental, and cultural injustices that have impacted health," Emerson notes. "As a result, many of these long-term exposures have resulted in an unequal contemporary burden of comorbid health conditions."
Significant increase in cancer mortality
Alongside comorbidity, the team looked at cancer survival rates. The most significant findings were regarding prostate cancer. The data showed that the AIAN community had an 87 percent increased risk of prostate cancer-specific mortality.
The AIAN group also had a 47 percent raised risk of all-cause mortality following invasive breast cancer. These figures remained significant, even after controlling for factors such as patient differences, income, characteristics of the disease, and comorbidity status.
However, in AIAN individuals, there was no significant increase in cancer-related mortality for lung or colorectal cancer.
"Our results suggest that factors other than health insurance and income may play a role in the survival differences observed for breast and prostate cancer. These factors could include differences in tumor biology or differences in aspects of treatment, such as adherence."
Marc A. Emerson
There were certain limitations to the study. As Habel notes, "The electronic health records do not have data on some lifestyles and behaviors that may have influenced cancer outcomes." Also, it was not possible to track how well each participant adhered to their treatment regimen.
If this increased risk is confirmed, future research will need to delve into the mechanisms that might be behind it, whether they are biological or behavioral. Understanding why risks might be higher in certain populations could lead to more successful treatment regimens.