Substantially increased risk of cancer in patients with diabetes mellitus: a systematic review and meta-analysis of epidemiologic evidence in Japan

Several meta-analyses have shown that diabetes mellitus affects the risk of certain site-specific cancers. However, a meta-analysis on the overall risk of cancer has not yet been performed. We performed a search of MEDLINE and the Cochrane Library for pertinent articles (including their references) that had been published as of June 10, 2010. English-language, original observational cohort studies and case-control studies conducted in Japan were included for a qualitative review and a meta-analysis. A total of 22,485 cancer cases were reported in four cohort studies and one case-control study (with a total of 250,479 subjects). With these five reports, a meta-analysis of the all-cancer risk in both men and women showed an increased risk in subjects with diabetes, compared with nondiabetic subjects (OR 1.70, 95% CI 1.38-2.10). The increase in the risk ratio adjusted for possible confounders was significant in men and borderline in women (adjusted RR 1.25, 95% CI 1.06-1.46 in men; adjusted RR 1.23, 95% CI 0.97-1.56 in women). An analysis of site-specific cancers revealed increased risks for incident hepatocellular cancer (OR 3.64, 95% CI 2.61-5.07) and endometrial cancer (OR 3.43, 95% CI 1.53-7.72). As is the case in Western countries, Asian people with diabetes have a higher risk of incident cancer than those without diabetes. Cancer prevention and early detection should be important components of diabetes management in light of the exponentially increasing prevalence of diabetes, which has substantial implications in public health and clinical practices.