OBJECTIVES : Based on some meta-analyses of observational studies and several RCT, it is not conclusive whether metformin use reduces cancer risk in type 2 diabetes. This study aimd to investigate whether use of anti-diabetic medication including metformin, sulfonylureas, thiazolidinediones, α-glucosidase inhibitors and insulin is associated with the overall and site-specific cancer risk, controlling for potential bias.

METHODS : Data were obtained from Tianjin Urban Employee Basic Medical Insurance database (2003-2014). Adult patients who were newly diagnosed with type 2 diabetes in 2009, and only used 1 class of anti-diabetic medication during the 1^st year follow-up were included and grouped accordingly. Newly-diagnosed patients who had no prescription of antidiabetic medication during the whole follow-up period were identified as the untreated group. Overall and 5 site-specific (stomach, colorectum, liver, lung, breast) cancer incidence rates were calculated for all 6 groups during follow-up. Multivariate Cox proportional hazards models adjusting for baseline characteristics were further conducted.

RESULTS : A total of 3901 diabetic patients were included (648 for untreated, 630 for metformin, 1053 for sulfonylureas, 159 for thiazolidinediones, 613 for α-glucosidase inhibitors, and 798 for insulin). The average ages were between 58.2 to 60.8 years across 6 groups. During the 5-year follow-up period, 161 patients were newly diagnosed with cancer, without significant differences of cancer incidence rates presented across 6 groups. Compared with the untreated group, the hazard ratios of overall cancer risk were 0.68 [95%CI: 0.38-1.23] for metformin, 0.87 [0.54-1.40] for sulfonylureas, 0.59 [0.21-1.70] for thiazolidinediones, 1.09 [0.65-1.83] for α-glucosidase inhibitors and 1.09 [0.66-1.81] for insulin group. Similar to the findings regard to overall cancer risk, no significant differences regard to site-specific cancer risk were detected across 6 groups.

CONCLUSIONS : No association was found between antidiabetic medication use and cancer risk among patients with newly-diagnosed type 2 diabetes in China.