Environmental and Nutritional Links to Esophageal Cancer Found Globally

Division of Cancer Epidemiology and Genetics

Christian Abnet, Ph.D., M.P.H., has literally traveled around the world in search of answers to questions about what causes esophageal and gastric (stomach) cancers. The investigator from NCI’s Nutritional Epidemiology Branch has focused his research sleuthing on high-risk populations for these diseases in China, Iran, Ireland, South America, and Africa.

The populations in those regions have little in common ethnically, culturally, or genetically, so Dr. Abnet tries to identify any “unifying theme” that might tie their high rates of cancer to shared risk factors. For example, people living in certain areas of China, Iran, and Brazil have moderate to very high rates of esophageal squamous cell carcinoma (ESCC). The connecting thread among these far-flung pockets of the disease may be high levels of human exposure to a group of compounds called polycyclic aromatic hydrocarbons (PAH), including the known carcinogen benzo[a]pyrene.

“In Linxian, China, the PAH exposures are from both cooking and heating,” Dr. Abnet explained. “They use coal and unventilated stoves, so they’re exposed directly to PAHs from breathing the coal smoke. They’re exposed indirectly from smoke deposits on their food.”

He and his colleagues are still trying to determine the source of high exposure to PAHs in northern Iran. However, in their studies in Brazil, where there are moderately high rates of ESCC, PAH exposure was surprisingly linked to drinking the popular regional beverage, maté– an herbal tea. “We’ve done some work to show that the amount of benzo[a]pyrene and other PAHs in maté is actually quite high,” Dr. Abnet said. With maté drinkers typically consuming one or more liters a day, their exposure levels can be substantial.

Dr. Abnet’s research is intended to have public health impact through prevention programs in areas of the world where resources for treating cancer and other serious diseases are limited.

“In China, there is the possibility for change in the way people cook and heat their homes, such as adding chimneys for their stoves,” he noted. In South America, “we found variations in the amount of PAHs in the different brands of maté,” Dr. Abnet recalled. “So it seems possible to find ways to process the plant leaves in a way that would lower PAH exposure in drinkers, or people may want to avoid drinking maté.”

Based on his and his colleagues’ earlier research in China, “We have clinical trial and observational epidemiological studies suggesting that the lack of selenium in the diet is a critical determinant of the high risk for ESCC in certain regions. Selenizing salt may be beneficial,” Dr. Abnet believes. “We’ve been discussing with our Chinese research colleagues whether or not it’s time for at least a demonstration project where they would selenize salt and look at how it affects the population’s levels of selenium and the subsequent cancer rates.”

To conduct this wide-ranging research, Dr. Abnet and his collaborators have “built population resources in different parts of the world where we’ve collected, either through case-control or cohort studies, large datasets and biospecimens for studying cancers in high-risk populations,” he said. “We have quite a few ongoing studies looking at several nutrients in addition to selenium. For example, in our study in China, we’re in the middle of a project to look at serum vitamin C status in relation to the risk of both ESCC and gastric cancer.”