Implications of Type1/2 Diabetes Mellitus in Breast Cancer Development: A General Female Population-based Cohort Study.

Aim: The current study assessed the potential impact of diabetes type 1 and type 2 for female breast cancer risk.
Materials and Methods: The health information and medical record of the entire adult female residents in Taiwan were retrieved from Taiwan's National Health Insurance Research Database. Multivariate Cox proportional hazard regression models and descriptive statistics were used to identify potential correlations between type 1/2 diabetes and breast cancer. In addition, this study statistically assessed the possible association of diabetes and breast cancer risk with age, insurance amount (quality of care), and regions.
Results: The diabetic status of the entire adult female population was assessed between 2001 and 2003. Of 10,827,079 adult females, 4,738 (0.04%) were diagnosed with type 1 and 830,546 (7.7%) with type 2 diabetes, and 9, 991,795 (92.3%) were free of diabetes. From 2004 to 2010, a total of 57,283 cases of breast cancer were detected, with an average breast cancer incidence rate of 0.53% in the generation population. The actual breast cancer incidence rate was 0.30% (14 of 4,738) in patients with type 1 diabetes, 1.10% (9,105 of 830,546) in patients with type 2 diabetes, and 0.48% (48,164 of 9,991,795) in patients free of diabetes. The breast cancer incidence rate is significantly higher (p < 0.001) in patients with type 2 diabetes than that in patients with type 1 diabetes and in patients free of diabetes. After adjusting for the covariates of age, insurance cost, and region, hazard ratios (HRs) for the association between breast cancer risk and types 1 and 2 DM were 1.01 (CI = 0.60-1.71) and 1.13 (CI = 1.10-1.16), respectively. Women with type 2 diabetes were at a significantly higher risk for development of breast cancer compared with those free of diabetes, but there appeared to have no significant increase in risk for those with type 1 diabetes. Our study also revealed that age, insurance amount (quality of care), and region are significantly associated with diabetes and breast cancer risk (p<0.0001).
Conclusion: Our results demonstrated different implications of diabetes type for the risk of breast cancer with type 2 posing a higher risk than type 1. This is the largest cohort study that assesses the possible correlation between both type 1 and 2 diabetes with breast cancer, and also is the largest cohort study showing that diabetes are associated with age, insurance, and region, which further suggest that living condition and life style may significantly associated with diabetes and breast cancer.