Risk factors for cancer development in type 2 diabetes: A retrospective case-control study.

BACKGROUND: The risk of several types of cancer is increased in type 2 diabetes mellitus. The earliest possible diagnosis of cancer - difficult within regular outpatient diabetes care - is of utmost importance for patients' survival. The aim of this multicenter, retrospective (years 1998-2015), case-control study was to identify risk factors associated with malignancy in subjects with diabetes treated in a typical outpatient setting.

METHODS: In the databases of 3 diabetic and 1 primary care clinics 203 patients (115 women) with type 2 diabetes mellitus who developed malignancy while treated for diabetes were identified. The control group consisted of 203 strictly age- and gender matched subjects with type 2 diabetes without cancer. Factors associated with diabetes: disease duration, antidiabetic medications use and metabolic control of diabetes were analyzed. Also other variables: BMI (body mass index), smoking habits, place of residence and comorbidities were included into analysis.

RESULTS: The most prevalent malignancies in men and women together were breast cancer (20.7 %) and colorectal cancer (16.3 %). HbA1c (hemoglobin A1c) level ≥8.5 %, obesity and insulin treatment in dose-dependent and time-varying manner demonstrated significant association with increased risk of malignancy, while metformin use was associated with a lower risk of cancer. Diabetes duration, comorbidities, smoking habits, place of residence and aspirin use did not show significant association with risk of malignancy.

CONCLUSIONS: In the outpatient setting the obese patients with poorly controlled insulin treated type 2 diabetes mellitus should be rigorously assessed towards malignancies, particularly breast cancer in women and colorectal cancer in men.