Long-term insulin glargine use raises the risk for breast cancer among women with type 2 diabetes, according to a study published in the Journal of Clinical Oncology.
In this population-based cohort study, investigators sought to determine the association between breast cancer and long-acting glargine (n=9575) or detemir (n=3271) vs neutral protamine Hagedorn (NPH) insulin (n=9549) in women treated for type 2 diabetes.
At 12 years, a total of 321 incident breast cancer events occurred in the overall cohort. Women receiving therapy with insulin glargine had an increased risk for breast cancer compared with patients who were receiving NPH insulin (hazard ratio [HR], 1.44; 95% CI, 1.11-1.85). The risk for breast cancer among women with type 2 diabetes increased primarily 5 years following initiation of glargine (HR, 2.23; 95% CI, 1.32-3.77) as well as following >30 prescriptions (HR, 2.29; 95% CI, 1.26-4.16).
Patients who had taken insulin prior to the study period were more likely to have a breast cancer diagnosis than new insulin users (HR, 1.53; 95% CI, 1.10-2.12). The investigators observed no significantly higher breast cancer risk among women taking insulin detemir (HR, 1.17; 95% CI, 0.77-1.77).
The investigators of this study suggest that unmeasured confounding, mainly because of the observational nature of the analysis, represents a potential study limitation.
Although these findings may warrant considerable caution against prescribing insulin glargine for women with type 2 diabetes, the investigators believe the risks and benefits of “insulin glargine must be considered by drug regulatory agencies before any changes to clinical practice can be made.”
Wu JW, Azoulay L, Majdan A, Boivin J-F, Pollak M, Suissa S. Long-term use of long-acting insulin analogs and breast cancer incidence in women with type 2 diabetes. J Clin Oncol. 2017;35:3647-3653.