The use of anastrozole for the prevention of breast cancer in postmenopausal women at increased risk of the disease was associated with a higher incidence of carpal tunnel syndrome (CTS), according to an exploratory analysis of data from the International Breast Cancer Intervention Study II. The results were published online ahead of print in the Journal of Clinical Oncology.1

CTS results when the median nerve is compressed at the wrist in the carpal tunnel. A higher incidence of CTS has been reported in randomized clinical trials with aromatase inhibitors (AIs). This study is the first to report risk factors for and characteristics of CTS in women taking an AI.

The International Breast Cancer Intervention Study II is a double-blind randomized clinical trial in which women at increased risk of breast cancer were randomly assigned to receive anastrozole or placebo.

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Overall, researchers observed 96 women with CTS; 65 women (3.4%) were in the anastrozole arm and 31 women (1.6%) were in the placebo arm (odds ratio, 2.16 [1.40 to 3.33]; P<.001). Severe CTS was reported in 10 women, of which eight were taking anastrozole (P=.08). Of the women in the anastrozole arm, 18 (0.9%) reported surgical intervention; 6 women (0.3%) in the placebo arm reported surgical intervention. Six women discontinued their treatment due to onset of CTS.

The only risk factors other than treatment allocation in these women were a high body mass index and a prior report of musculoskeletal symptoms after trial entry.


1. Spagnolo F, Sestak I, Howell A, Forbes JF, Cuzick J. 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.