Trends in breast cancer incidence among women with type-2 diabetes in British general practice.

Abstract

To quantify breast cancer incidence in women with type-2 diabetes and assess age-standardized trends in invasive breast cancer incidence over time and by age groups. A population-based cohort study was conducted using the British general practice database (Clinical Practice Research Datalink) using data from 1989 to 2012. All adult women prescribed anti-hyperglycemic medication were selected and matched (1:1) on age and clinical practice to a reference cohort without diabetes. During approximately 1.6 million person years (py), 2371 breast cancer cases were diagnosed in the diabetes cohort (n=147,998) and 2252 in the reference cohort (n=147,998). Incidence of breast cancer, overall or by age groups, among women with diabetes remained stable over time. The (overall) age-standardized breast cancer IR per 100,000 py of the diabetes cohort (150, 95%CI:143-157) resembled that observed in the reference cohort (148, 95%CI:141-156); with an incidence rate ratio (IRR) of 1.01 (95%CI:0.94-1.08, p>0.05). Currently, around 2880 women with type-2 diabetes are diagnosed with breast cancer per year in the United Kingdom. However, breast cancer incidence remained stable in the last 10 years and seems to be comparable in women with and without diabetes.