Impact of coexisting diabetes on survival and risk of developing second primary cancer in diabetes patients receiving drug therapy: A multicenter retrospective cohort study of patients with cancer in Japan

AIMS/INTRODUCTION: We investigated the association between coexisting diabetes at the time of cancer diagnosis, and the overall survival and incidence of second primary cancer in patients with cancer and receiving drug therapy for diabetes. MATERIALS AND METHODS: We used cancer registry and administrative data of patients diagnosed with cancer at designated cancer care hospitals in Osaka Prefecture between 2010 and 2015. The presence of diabetes was identified from the prescription records of antidiabetic drugs in Diagnosis Procedure Combination System data. After adjusting for patient characteristics, we compared overall survival between patients with cancer with coexisting diabetes and those without coexisting diabetes using the Cox proportional hazards model. In addition, the impact of coexisting diabetes on the risk of developing second primary cancer was evaluated using a competing risk analysis. RESULTS: Of the 131,701 patients with cancer included in the analysis, 6,135 (4.7%) had coexisting diabetes. The 5‐year survival rates for patients with and without coexisting diabetes were 56.2% (95% confidence interval 54.8–57.6) and 72.7% (95% confidence interval 72.4–73.0), respectively. Coexisting diabetes was associated with a higher risk of developing second primary cancer (subdistribution hazard ratio 1.23; 95% confidence interval 1.08–1.41). In site‐specific analysis, coexisting diabetes was associated with an increased risk for the development of second primary cancer of multiple myeloma, and cancer of the uterus, pancreas and liver. CONCLUSIONS: Coexisting diabetes was associated with a higher mortality and risk of developing second primary cancer in Japanese patients with cancer and on drug therapy for diabetes.