Impact of metformin on metastases in patients with breast cancer and type 2 diabetes

AimTo analyze the impact of glucose-lowering drugs on metastases in women living in Germany who have been diagnosed with breast cancer (BC) and type 2 diabetes mellitus (T2DM).MethodsWomen initially diagnosed with BC (2004-2013) were identified in the IMS Disease Analyzer database. Patients with a documentation of metastases at index date or during the following six months were excluded. We selected T2DM women between 40 and 90 years of age who received glucose-lowering therapy (metformin, sulfonylureas, incretins, insulins, other medications). The primary outcome was the diagnosis of metastases recorded in the database between the index date and the end of follow-up. A multivariate Cox regression model was used to predict BC metastases on the basis of patient characteristics and glucose-lowering medication.ResultsA total of 4,953 women with BC and diabetes were included in the study. The mean age was 71.4 years and 4.7% of patients had private health insurance coverage. Mean HbA1C was 7.1% and mean BMI was 30.6 kg/m2. After 5 years follow-up, 9.2% of patients with metformin and 12.3% of patients without exhibited metastases (log-rank p-value = 0.011), whereas 6.2% of patients with incretins and 11.0% of patients without incretins exhibited metastases (both log-rank p-values < 0.001). Metformin (HR = 0.73, 95% CI: 0.58-0.92) and incretins (HR = 0.62, 95% CI: 0.45-0.84) both significantly decreased the risk of metastases. None of the other variables were significantly associated with diagnosis of metastases.ConclusionThe use of metformin and incretins in women with T2DM and BC may reduce the risk of metastases.