The incidence rate of hepatocellular carcinoma in urban areas of the United States began to slow in 2009, but the rate in rural areas of the nation continued to rise at a steady pace, especially among non-Hispanic Whites and Blacks, investigators have found.
Although overall hepatocellular carcinoma (HCC) incidence rates were consistently lower among people living in nonmetro (rural) versus metro (urban) areas, the average annual percentage change in urban areas began to slow from 5.3% for the period of 1995 through 2009 to 2.7% thereafter. In contrast, the average annual percentage change in rural areas remained steady at 5.7%, a disparity that remained even after adjusting for differences among subgroups, reported Christina Gainey, MD, a third-year resident in internal medicine at the University of Southern California Medical Center, Los Angeles.
“We found that there are striking urban-rural disparities in HCC incidence trends that vary by race and ethnicity, and these disparities are growing over time,” she said during the virtual annual meeting of the American Association for the Study of Liver Diseases.
“Our study really highlights a critical public health issue that’s disproportionately affecting rural Americans. They already face considerable health inequities when it comes to access to care, health outcomes, and public health infrastructure and resources, and as of now we still don’t know why cases of HCC continue to rise in these areas,” she said.
Dr. Gainey noted that HCC is the fastest-growing cancer in the United States, according to the 2020 Annual Report to the Nation on the Status of Cancer, issued jointly by the Centers for Disease Control and Prevention, the North American Association of Central Cancer Registries, the American Cancer Society, and the National Cancer Institute.
Previous studies have identified disparities between urban and rural regions in care of patients with cervical cancer, colorectal cancer, and other malignancies, but there are very few data on urban-rural differences in HCC incidence, she said.
Incidence trends
To better understand whether such differences exists, the investigators compared trends in age-adjusted incidence rates of HCC in both rural and urban areas of the United States from 1995 to 2016, with stratification of trends by race/ethnicity and other demographic factors.
They drew from the NAACR database, which captures 93% of the U.S. population, in contrast to the CDC’s Surveillance, Epidemiology, and End Results (SEER) database which samples just 18% of the population.
Patients with HCC were defined by diagnostic codes, with diagnoses of intrahepatic bile duct cancers excluded.
They used 2013 U.S. Department of Agriculture Rural-Urban Continuum Codes to identify rural areas (regions of open countryside with town populations fewer than 2,500 people) and urban areas (populations ranging from 2,500 to 49,999, but not part of a larger labor market area).
The investigators identified a total of 310,635 HCC cases, 85% in urban areas and 15% in rural areas. Three-fourths of the patients (77%) were male. The median age ranged from 55-59 years.
There were notable demographic differences between the regions with non-Hispanic Whites comprising only 57% of the urban sample, but 82% of the rural sample. The urban sample included 16% non-Hispanic Blacks, 10% Asian/Pacific Islanders, and 17% Hispanics. The respective proportions in the rural areas were 8%, 2%, and 8%.
As noted before, age-adjusted incidence rates (adjusted to the year 2000 U.S. population) were lower in rural areas, at 4.9 per 100,000 population, compared with 6.9/100,000 in urban areas.
But when they looked at the average annual percentage changes using jointpoint regression, they saw that beginning in 2009 the AAPC in urban areas began to slow, from 5.3% for the period prior to 2009 to 2.7% thereafter, while the average annual percentage change in urban areas remained steady at 5.7%.
The largest increase in incidence over the course of the study was among rural non-Hispanic Whites, with an AAPC of 5.7%. Among urban non-Hispanic Blacks, the AAPC rose by 6.6% from 1995 to 2009, but slowed thereafter.
In contrast, among rural non-Hispanic Blacks the AAPC remained steady, at 5.4%.
The only group to see a decline in incidence was urban Asians/Pacific Islanders, who had an overall decline of 1%.
Among all groups, rural Hispanics had the highest age-adjusted incidence rates, at 14.9 per 100,000 in 2016.
Awareness gap?
Lewis R. Roberts, MB, ChB, PhD, a hepatobiliary cancer researcher at the Mayo Clinic in Rochester, Minn., who was not involved in the study, said in an interview that the difference in incidence rates between cities and the country may be attributable to a number of factors, including the opioid crisis, which can lead to an increase in injectable drug use or sexual behaviors resulting in increases in chronic hepatitis C infections and cirrhosis, known risk factors for HCC, as well as a lack of awareness of infections as a risk factor.
“In order for people to find these diseases, they have to be looking, and many of these are hidden diseases in our community,” he said. “What the study made me wonder was whether it just happens to be that they are in some ways more hidden in a rural community than they are in an urban community.”
He noted that clinicians in urban communities are more accustomed to treating more diverse populations who may have higher susceptibility to viral hepatitis, for example, and that screening and treatment for hepatitis C may be more common in urban areas than rural areas, he said.
No funding source for the study was reported. Dr. Gainey and Dr. Roberts reported having no conflicts of interest to disclose.
SOURCE: Gainey C et al. Liver Meeting 2020, Abstract 136.