Anastrozole-Induced Carpal Tunnel Syndrome: Results From the International Breast Cancer Intervention Study II Prevention Trial

Purpose Carpal tunnel syndrome (CTS) occurs when the median nerve is compressed at the wrist in the carpal tunnel. It has been suggested that hormonal risk factors may be involved in the pathogenesis of CTS, and a higher incidence of CTS has been reported in randomized clinical trials with aromatase inhibitors (AIs) compared with tamoxifen. Patients and Methods This was an exploratory analysis of the International Breast Cancer Intervention Study II, a double-blind randomized clinical trial in which women at increased risk of breast cancer were randomly assigned to receive anastrozole or placebo. This is the first report of risk factors for and characteristics of CTS in women taking an AI in a placebo-controlled trial. Results Overall, 96 participants with CTS were observed: 65 (3.4%) in the anastrozole arm and 31 (1.6%) in the placebo arm (odds ratio, 2.16 [1.40 to 3.33]; P<.001). Ten participants were reported as having severe CTS, of which eight were taking anastrozole (P = .08). Eighteen women (0.9%) in the anastrozole arm and six women (0.3%) in the placebo arm reported surgical intervention, which was significantly different (odds ratio, 3.06 [1.21 to 7.72], P = .018). Six women discontinued with the allocated treatment because of the onset of CTS. Apart from treatment allocation, a high body mass index and an a prior report of musculoskeletal symptoms after trial entry were the only other risk factors for CTS identified in these postmenopausal women. Conclusions The use of anastrozole was associated with a higher incidence of CTS but few participants required surgery. Further investigations are warranted into the risk factors and treatment of AI-induced CTS. (C) 2015 by American Society of Clinical Oncology