Anastrozole use for the prevention of breast cancer in women with an increased risk of breast cancer was associated with a higher incidence of carpal tunnel syndrome, a new study published online ahead of print in the Journal of Clinical Oncology has shown.1

Carpal tunnel syndrome, which occurs when the median nerve is compressed at the wrist in the carpal tunnel, may be caused by hormonal risk factors. Because a higher incidence of carpal tunnel syndrome has been reported in clinical trials with aromatase inhibitors compared with tamoxifen, researchers sought to evaluate whether anastrozole treatment increases the risk of carpal tunnel syndrome.

Researchers analyzed data from the International Breast Cancer Intervention Study II, a double-blind clinical trial that randomly assigned women at increased risk of breast cancer to receive anastrozole or placebo.

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Results showed that 3.4% of patients in the anastrozole arm and 1.6% of those in the placebo arm developed carpal tunnel syndrome (OR, 2.16; 95% CI, 1.40 – 3.33; P < .001). Researchers found that few participants required surgery.

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The study also demonstrated an association between high body mass index and a prior history of musculoskeletal symptoms after trial entry and an increased risk for carpal tunnel syndrome in postmenopausal patients.

“Further investigations are warranted into the risk factors and treatment of AI-induced [carpal tunnel syndrome],” the authors concluded.


  1. Spagnolo F, Sestak I, Howell A, et al. Anastrozole-induced carpal tunnel syndrome: results from the International Breast Cancer Intervention Study II Prevention trial [published online ahead of print November 23, 2015]. J Clin Oncol. doi: 10.1200/JCO.2015.63.4972.