Diabetes History and Gastric Cancer Risk: Different Results by Types of Follow-Up Studies

Objective: The previous systematic reviews evaluating the association between diabetes history and gastric cancer risk showed inconsistent results. The aim was to check through a meta-epidemiological study that the conclusions of systematic reviews evaluating the association between diabetes history and gastric cancer risk might differ by the type of follow-up study. Methods: The potential study subjects were follow-up studies selected from the seven systematic reviews obtained by searching PubMed using diabetes and gastric cancer keywords. The selection criterion was defined as a follow-up study for evaluating the association between the history of type 2 diabetes mellitus and the incidence of gastric cancer. And the values of RR and its 95%CI, which adjusted for the most confounders in each paper, were extracted for meta-analysis. A random-effects model meta-analysis by types of the follow-up study and sex group was performed. Results: A total of 25 follow-up studies were finally selected for meta-analysis. They were classified into 16 retrospective and 9 prospective studies in types of follow-up study. The statistical significance between diabetes history and gastric cancer risk was found in retrospective studies (sRR=1.17, 95%CI: 1.02-1.34, I-squared =91.0%) but disappeared in prospective studies (sRR=1.09, 95%CI: 0.91-1.29, I-squared = 68.6%). Even in the analysis of subgroups by sex, statistical significance was not found in the prospective study, consistently. Conclusion: The main reason for the previous meta-analysis’s diverse results for the association between diabetes history and gastric cancer risk was that the type of follow-up study was not reflected. According to the meta-analysis of prospective cohort studies, it could be concluded that there is no association between diabetes history and gastric cancer risk.