Abstract P4-12-07: Diabetes Increases the Risk of Breast Cancer

Abstract

Abstract Background: The hyperinsulinaemia associated with type 2 diabetes and the known proliferative effects of insulin lead to the hypothesis that diabetes mellitus increases the risk of breast cancer. The aim of this meta-analysis was to collate and analyse all primary observational studies investigating the risk of breast cancer associated with diabetes. In addition, we aimed to complete sub group analyses by both type of diabetes and gender of study participants to further clarify the origin of any such association between the two. Method: Studies were obtained from a database search of MEDLINE, EMBASE, PubMed, Current Contents Connect and Google Scholar with additional cross checking of reference lists. Databases were searched using subject headings, keyword searches and text word searches wherever possible using the search terms ‘diabetes’ AND ‘breast cancer’ OR ‘breast carcinoma’ OR ‘breast neoplasm’. Inclusion criteria required a confirmed diagnosis of both diabetes and breast cancer, reporting of an odds ratio or data to calculate an unadjusted odds ratio (and 95% confidence interval) and the use of an internal control group as the comparator. Collated data was assessed for heterogeneity and a pooled odds ratio calculated. Results: 34 studies were included in the meta-analysis with 31 studies investigating breast cancer in women and 5 studies investigating breast cancer in men. Overall, we found a significantly increased risk of breast cancer associated with diabetes in both women (OR 1.25, 95% CI 1.13–1.38) and men (OR 1.40, 95% CI 1.10–1.79). The pooled odds ratio was consistent across both case control studies (OR 1.25, 95% CI 1.06–1.46) and cohort studies (OR 1.26, 95% CI 1.09–1.45). Heterogeneity was significant (I2 = 73.40, p < 0.001) and publication bias was present (p = 0.03). The 31 studies investigating breast cancer in women were sub grouped by type of diabetes with the association strengthened by a diagnosis of type 2 diabetes (OR 1.32, 95% CI 1.09–1.61) but nullified with gestational diabetes (OR 1.06, 95% CI 0.79–1.40). There were insufficient studies to calculate a pooled odds ratio of the risk of breast cancer associated with type 1 diabetes. Conclusion: Diabetes increases the risk of breast cancer in both women and men. This association is strengthened in women with type 2 diabetes and supports the hypothesis that diabetes is an independent risk factor for breast cancer. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-12-07.