Women with type 2 diabetes may have an increased risk of breast cancer with the long-term use of insulin glargine, according to a study published in the Journal of Clinical Oncology.1

Previous studies investigating the association of long-acting insulin analogues and increased breast cancer risk have been mixed, and the follow-up periods for these studies have been too short to lead to any definitive conclusions.

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For this population-based cohort, researchers identified 22,395 women aged 40 years and older who received at least 1 prescription of insulin glargine, detemir, and neutral protamine Hagedorn (NPH) from the United Kingdom Clinical Practice Research Datalink.

During the 12-year follow-up period, 321 patients developed breast cancer. Women received averages of 5.4, 5.4, and 5.8 prescriptions of insulin glargine, detemir, and NPH, respectively, per year throughout the follow-up period.

Compared with patients on NPH insulin, women receiving insulin glargine had an increased risk of breast cancer (hazard ratio [HR], 1.44; 95% CI, 1.11-1.86), which increased primarily 5 years after initiating insulin glargine (HR, 2.23; 95% CI, 1.32-3.77), and after more than 30 filled prescriptions (HR, 2.29; 95% CI, 1.26-4.16).

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No increase in risk was observed among patients who received insulin detemir in comparison with NPH insulin (HR, 1.17; 95% CI, 0.77-1.77).

The data suggest that the risk was higher among patients who were prior users of insulin glargine (HR, 1.53; 95% CI, 1.10 – 2.12) but not for new users of insulin (HR, 1.18; 95% CI, 0.77-1.81), and only prior users had an association with duration and dose-response. The authors did note, however, that the data pool was smaller for new users.

The authors concluded that “despite these findings, the benefits and risks of insulin glargine must be considered by drug regulatory agencies before any changes to clinical practice can be made.”


  1. Wu JW, Azoulay L, Majdan A, Boivin JF, 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 Sep 27. doi: 10.1200/JCO.2017.73.4491 [Epub ahead of print]