Long-Term Use of Long-Acting Insulin Analogs and Breast Cancer Risk in Type 2 Diabetes

Key Points

  • In women with type 2 diabetes, use of insulin glargine was associated with a significantly increased breast cancer risk vs NPH insulin.
  • A nonsignificant increase in risk was observed for insulin detemir use.

A study in the UK population has shown that long-term use of the long-acting insulin glargine was associated with increased risk of breast cancer among women with type 2 diabetes. The findings were reported by Wu et al in the Journal of Clinical Oncology.

Study Details

The study involved a population-based cohort of 22,395 women aged ≥ 40 years treated with long-acting (glargine, detemir) or neutral protamine Hagedorn (NPH) insulin between 2002 and 2012 derived from the United Kingdom’s Clinical Practice Research Datalink. Women were followed until February 2015 or breast cancer diagnosis. Among the 22,395 women, 9,575, 3,271, and 9,549 used insulin glargine, insulin detemir, and NPH, respectively. Overall, there were 321 incident breast cancer cases during up to 12 years of follow-up (incidence rate = 3.3 per 1,000 person-years).

Risk With Long-Acting Analogs

Compared with NPH insulin, insulin glargine use was associated with an increased risk of breast cancer (hazard ratio [HR] = 1.44, 95% confidence interval [CI] = 1.11–1.85), with risk increasing primarily 5 years after insulin glargine initiation (HR = 2.23, 95% CI = 1.32–3.77) and after > 30 prescriptions (HR = 2.29, 95% CI = 1.26–4.16). In a sensitivity analysis, the association of insulin glargine with breast cancer was higher among prior insulin users (57% of patients; HR = 1.53, 95% CI = 1.10–2.12) than among new insulin users (HR = 1.18, 95% CI = 0.77–1.81). Risk associated with insulin detemir use vs NPH insulin was not significantly elevated (HR = 1.17, 95% CI = 0.77–1.77).

The investigators concluded: “Long-term use of insulin glargine is associated with an increased risk of breast cancer in women with type 2 diabetes. The risk associated with insulin detemir remains uncertain because there are fewer users of this insulin.”

The study was funded in part by infrastructure grants from the Canadian Institutes of Health Research and the Canadian Foundation for Innovation.

Samy Suissa, PhD, of McGill University, is the corresponding author of the Journal of Clinical Oncology article.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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