CARING: Diabetes mellitus and risk of cancer: A systematic review and meta-analysis

Background and aims: Patients suffering from diabetes mellitus (DM) may experience an increased risk of cancer, but results are conflicting. The aim is to examine the association between DM and cancer by a meta-analysis. Materials and methods: A systematic review and meta-analysis was performed according to the PRISMA guidelines. The systematic literature search included Pubmed, Embase, Cinahl, Bibliotek.dk, Cochrane library, Web of Science and Svemed+ with the search terms: “Diabetes mellitus”, “Neoplasms”, “Prospective study” and “Risk of cancer”. Odds ratios, relative risks, risk ratios, hazard ratios, prevalence ratios, incidence ratios and standardized incidence ratios were used in the pooled analysis. Statistical analysis was performed using random effects models. Results: A total of 1,785 records were screened by title and abstract and 253 records were subsequently assessed by full text, of which 195 records fulfilled the criteria for the systematic review. The cancer types studied showed significant heterogeneity across studies by Chi-square test.Compared to nondiabetic controls, DM patients had an increased risk of any cancer (RR=1.14, 95 % CI [1.01-1.28], 26 records). Diabetics seemed especially at risk of liver (RR=2.27, [1.86-2.78], 47 records), pancreas (RR=2.21 [1.86-2.62], 47 records) and endometrial cancer (RR=1.9, [1.67-2.16], 24 records), although an increased risk was also seen for biliary tract, stomach, colon, rectum, kidney, bladder, breast and thyroid gland cancer. In contrast, DM patients appeared to experience a decreased risk for prostate cancer (RR= 0.87 [0.81-0.93], 44 records). Conclusion: DM patients were at higher risk of cancer than non-diabetics, especially digestive tract cancers and hormone/related cancers (breast, endometrial). However, an apparent protective effect against prostate cancer was present. The observed effects could be due to confounding by factors not adequately adjusted for in the studies like obesity.