Diabetes and gastric cancer: The potential links

Table 1 Main findings in four meta-analyses on the association between diabetes and incidence or mortality of gastric cancer

Ref.	Studies included	Summary RR (95%CI)		Notes and comments for specific studies	Limitations common to the meta-analysis studies
		Overall	Subgroup analysis
Ge et al[33], 2011	4 case-control and 17 cohort	1.09 (0.98-1.22)	Women: 1.18 (1.01-1.39)Men: 1.04 (0.94-1.15)Duration of follow-up < 10 yr: 0.95 (0.72-1.26)Duration of follow-up ≥ 10 yr: 1.14 (1.01-1.29)	Evaluating incidence and mortality togetherA mixture of incidence and mortality studies may not be appropriateEthnicity differences not considered	Heterogeneity in terms of study design, population demographics, diabetes ascertainment, duration of follow-up, and confoundersType 1 and type 2 diabetes not distinguished in most studiesCardia and non-cardia gastric cancer not discerned in most studiesConfounding effects of H. pylori, smoking and diet are not considered in most studiesNumbers of studies in subgroup analyses varied and may be too small for some analysesMost studies included in meta-analyses were conducted in developed western countries and not primarily designed for evaluating the association between diabetes and gastric cancerPublication bias is possible
Marimuthu et al[34], 2011	20 population-based cohort	Incidence: 1.01 (0.90-1.11)Mortality: 1.62 (1.36-1.89)	Type 1 diabetes (incidence): 1.60 (0.56-2.64)Asians (mortality): 1.98 (1.57-2.39)	Evaluating incidence and mortality separately in overall analysisConsidering type 1 diabetes and ethnicity differences in subgroup analyses
Tian et al[35], 2012	7 case-control and 18 cohort	Incidence: 1.11 (1.00-1.24) Mortality: 1.29 (1.04-1.59)	Asians: 1.19 (1.07-1.32)Cohort design: 1.14 (1.01-1.30) Type 2 diabetes: 1.16 (1.01-1.33) Studies adjusted for more confounders: 1.16 (1.03-1.30)	Evaluating incidence and mortality separately in overall analysisSubgroup analysis was conducted with a mixture of incidence and mortality
Yoon et al[36], 2013	6 case-control and 11 cohort	1.19 (1.08-1.31)	Cohort design: 1.20 (1.08-1.34)Case-control design: 1.12 (0.87-1.45)East Asian countries: 1.19 (1.02-1.38)Western countries: 1.18 (1.03-1.36)Men: 1.10 (0.97-1.24)Women: 1.24 (1.01-1.52)Studies adjusted for smoking: 1.17 (1.01-1.34)Studies adjusted for infection of H. pylori: 2.35 (1.24-4.46)Cardia cancer: 1.39 (0.72-2.69)Noncardia cancer: 1.19 (0.80-1.77)	Evaluating only incidenceStrengths include considering subgroup analyses in studies with adjustment for smoking and H. pylori infectionSubgroup analyses on cardia and noncardia cancer are available, but only 2 studies are included

H. pylori: Helicobacter pylori.