Objective: In Orientals, deficient aldehyde dehydrogenase 2 (ALDH2) is associated with an increased risk for esophageal squamous cell carcinoma (ESCC). The local metabolism of carcinogenic acetaldehyde in the upper gastrointestinal tract could be involved in the association, but the underlying mechanism has not been fully elucidated. Since an anacidic stomach can promote bacteria-catalyzed local acetaldehyde production, the gastric acid level could also affect acetaldehyde metabolism. This study investigated whether ALDH2-related susceptibility to ESCC differs depending on the gastric secretion level.
Material and methods: Sixty-two patients with ESCC and sex- and age-matched normal controls were enrolled in this study. ALDH2 polymorphism was analyzed by polymerase chain-restriction fragment length polymorphism, and those with an inactive allele (ALDH2-1/2-2 or ALDH2-2/2-2) were defined as ALDH2 deficient. Gastrin-stimulated acid output was assessed by endoscopic gastrin test and hypochlorhydria was defined as 0.6 mEq/10 min or lower. Multiple logistic regression analyses were used to adjust for other potential confounders.
Results: ALDH2 deficiency or hypochlorhydria was more prevalent in ESCC compared with controls and both showed increased independent associations with ESCC in multivariate analysis. Stratified analysis by the gastric acid secretion level revealed that the associations between the ALDH2 genotype and ESCC differed according to the individual gastric acid secretion levels and that ALDH2 deficiency was a significant risk factor for ESCC exclusively in individuals with hypochlorhydria with an odds ratio (95% confidence interval): 5.0 (1.2-21.2).
Conclusion: Microbial production of carcinogen acetaldehyde in the presence of gastric hypochlorhydria is most probably involved in the mechanism of ALDH2-related susceptibility to ESCC.