Geographic dimensions of gastric cancer risk in western Honduras: A spatial ecological analysis

Gastric cancer is fifth most common cancer globally, with a complex and multifactorial etiology, including human and bacterial genetics, health behaviors, and environmental exposures. Honduras has among the highest rates of gastric cancer in the western hemisphere, and previous research indicates that gastric cancer risk varies geographically at a sub-national scale. We analyzed characteristics of all 788 incident cases diagnosed in western Honduras between 2002 and 2015 for which residence information was available to assess geographic patterns of excess risk and population-level risk factors. We built hierarchal Bayesian Poisson models to implement spatial ecological analysis stratified by sex and gastric cancer sub-type (diffuse, intestinal, mixed/indeterminate) to explore sex and sub-type specific etiologies. We identified differential geospatial patterns of high observed relative risk (i.e., greater than 1.0) for across male/female and diffuse/intestinal strata. Unexplained variance was more spatially structured in models for males, but less so among females, suggesting that unobserved, spatially autocorrelated factors contributing to geographic risk patterns among males in this area. Additionally, ecological associations varied by sex/sub-type strata. Among males, risk of intestinal gastric cancer was elevated with an increase in the percentage of indigenous Maya/Chortí in the population, but this association was not detected in female strata. Our findings demonstrated substantial differences in geographic patterns of risk across sex and ancestry, which implicated that unobserved, sex-stratified factors, such as germline mutations and behaviors, play a role in shaping geographic patterns of cancer risk at the subnational level in western Honduras.