Long-Term Use of Insulin Glargine May Be Linked to Higher Risk of Breast Cancer

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A number of studies have suggested a link between diabetes, diabetes medicines, and breast cancer risk. Research strongly suggests that women diagnosed with diabetes are more likely to be diagnosed with breast cancer than women who aren’t diabetic.

A study suggests that women with type 2 diabetes who are treated long-term with a long-acting type of insulin called glargine (brand names include Lantus and Toujeo) may have a higher risk of breast cancer.

The study was published online on Sept. 27, 2017 by the Journal of Clinical Oncology. Read the abstract of “Long-Term Use of Long-Acting Insulin Analogs and Breast Cancer Incidence in Women With Type 2 Diabetes.”

Insulin glargine is a long-acting, man-made version of human insulin.

To do the study, researchers in the United Kingdom identified 22,395 women age 40 and older who were diagnosed with type 2 diabetes and had been treated with either:

  • insulin glargine
  • insulin detemir, also a long-acting man-made version of human insulin
  • neutral protamine Hagedorn (NPH) insulin, an intermediate-acting, man-made version of human insulin

between 2002 and 2012.

The women were followed until February 2015

Overall:

  • 9,575 women were treated with insulin glargine
  • 3,271 women were treated with insulin detemir
  • 9,549 women were treated with NPH insulin

On average, the women received between five and six prescriptions for the type of insulin they were being treated with per year.

During follow-up, 321 breast cancers were diagnosed:

  • 176 women treated with insulin glargine were diagnosed with breast cancer
  • 108 women treated with NPH insulin were diagnosed with breast cancer
  • 37 women treated with insulin detemir were diagnosed with breast cancer

Compared to women treated with NPH insulin, women treated with insulin glargine were 44% more likely to be diagnosed with breast cancer. The risk of breast cancer started to increase 5 years after the women started being treated with insulin glargine and after they had filled more than 30 prescriptions of insulin glargine.

Compared to women treated with NPH insulin, the researchers found no increase in breast cancer risk among women treated with insulin detemir. Still, the number of women treated with insulin detemir in the study was small, so the results might have been different if there were more data.

The researchers said the data suggest that the risk of breast cancer was higher among women who had previously used insulin glargine, but not for new users of insulin. Still, the number of new insulin users in the study also was small, so these results also might have been different if there were more data.

The researchers pointed out that “despite the results of the study, the benefits and risks of insulin glargine must be considered before any changes to clinical practice can be made.”

Other research suggests that diabetic women taking the medicine metformin (brand names: Fortamet, Glucophage, Glumetza, Riomet), which is commonly used to treat type 2 diabetes, have a lower-than-average risk of breast cancer.

If you have type 2 diabetes, you may want to talk to your endocrinologist about this study. If you use insulin glargine to manage the diabetes, it might make sense to ask your doctors if another type of insulin or metformin could be a better choice for you. Together, you and your doctors can figure out the best way to manage the diabetes and keep your risk of breast cancer as low as it can be.


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