Type 2 diabetes, insulin treatment and prognosis of breast cancer

Background The aim of our study was to investigate whether pre-existing type 2 diabetes and insulin therapy have an impact on the prognosis of breast cancer patients. Methods We performed a retrospective analysis of 462 type 2 diabetic breast cancer patients and 1644 non-diabetic breast cancer patients treated in our institute from January 2005 to August 2010. Patients were divided by diabetes status and insulin use. The clinicopathological characteristics and clinical outcomes of patients within 5 years following breast cancer diagnosed were analysed. Results Diabetic patients tended to have higher body mass index and higher histological grade tumours. Five-year disease-free survival and overall survival were reduced in diabetic patients (P<0.001), and diabetes was an independent predictor for an increased risk of breast cancer relapse and death within 5 years (P<0.001). Insulin treatment was associated with reduced 5-year disease-free survival and overall survival (P<0.05); the risk of 5-year relapse and breast cancer mortality in the insulin group increased compared to that of non-insulin group after adjusting for age, tumour size, histological grade, oestrogen receptor, progesterone receptor, chemotherapy and hormone therapy (P<0.05). After adjusting for age and other factors, the risk of breast cancer relapse was also increased in the insulin subgroup, while the risk of breast cancer mortality did not increase statistically. Conclusions Type 2 diabetes and insulin treatment might be independently associated with poorer prognosis of breast cancer. However, caution is needed when interpreting our results, and further investigations are needed. Copyright (C) 2016 John Wiley & Sons, Ltd.