Immigrants from countries with high rates of gastric cancer continue to experience greater morbidity and mortality from the disease after moving to the U.S., according to a review and meta-analysis co-led by Baldeep Pabla, M.D., and Shailja Shah, M.D., clinical investigators in the Division of Gastroenterology, Hepatology and Nutrition at Vanderbilt University Medical Center.
Their findings are reflected in the first evidence-based clinical practice guidelines for surveillance of gastric precancerous lesions by the American Gastroenterological Association (AGA).
“The racial and ethnic disparities underlying gastric cancer epidemiology in the U.S. just haven’t been on the radar for most health care providers,” Pabla said.
“The racial and ethnic disparities underlying gastric cancer epidemiology in the U.S. just haven’t been on the radar for most health care providers.”
A Global Concern
According to AGA guidelines, gastric cancer is the third leading cause of cancer deaths worldwide. About one million cases occur each year, with most arising in East Asia, Latin America, and Eastern Europe. While incidence of the disease is overall low in the U.S., rates are approximately double in Hispanic and non-Hispanic black populations, and even higher in some Asian American groups.
The study involved several goals, Pabla explained. “First, we wanted to see if we could demonstrate increased risk of gastric cancer in immigrants moving from high-risk to low incidence countries, as well as define the magnitude of this risk.” The researchers also wanted to test whether targeted gastric cancer screening and surveillance of precancerous lesions might be worthwhile in the U.S. Prior research has demonstrated the cost-effectiveness of such an approach for high-risk racial and ethnic groups.
The researchers identified 38 eligible studies that provided risk and/or mortality estimates for gastric cancer among immigrants. They focused on people who immigrated from regions of high gastric cancer incidence to regions of low gastric cancer incidence. Only five studies demonstrated no increased risk for immigrants.
In results published in Clinical Gastroenterology and Hepatology, the team calculated standardized incidence ratios and mortality ratios for gastric cancer among first-generation immigrants moving from high- to low-risk regions. Their calculations confirmed that gastric cancer cases and related deaths among the immigrant subgroups differed significantly from rates in the destination country overall.
In 13 of the studies whose cumulative findings generally reflected the meta-analysis findings, immigrants from high-incidence countries were at up to five times greater risk of developing gastric cancer than native-born residents in their new country.
Second-generation immigrants continued to have an elevated risk for gastric cancer, though not to as great a degree as their first-generation parents, supporting a role for non-genetic environmental or microbial factors in mediating gastric cancer risk.
Increased risk among immigrants is modulated by the degree to which the immigrants adopt the lifestyle and health behaviors of the host (low incidence) country, Pabla says. If a high-risk diet remains common among an immigrant group, it could contribute to their elevated risk.
“The overall risk of gastric cancer is higher when people have high intakes of salt and of nitrate-rich foods,” Pabla said, pointing particularly to a heavy emphasis on fermented foods in the Korean diet, as one example. Pabla notes fresh fruits and vegetables, on the other hand, appear to be protective.
Gastroenterologists in low-risk countries such as the U.S. need to become more aware of patients who have immigrated from high-risk countries, Pabla says, emphasizing the importance of inquiring about family history, prior testing and potentially modifiable factors, such as Helicobacter pylori infection or smoking.
Pabla is hopeful that the AGA’s new guidelines on gastric pre-cancer surveillance will usher change, by urging consideration of a patient’s ethnicity and immigration history as part of shared decision making. Currently, there are no U.S.-based guidelines for gastric cancer screening, although screening routinely occurs in higher-risk countries, such as Japan and South Korea.