Observational Study to Evaluate Mechanisms of Aromatase Inhibitor Associated Musculoskeletal Symptoms

Early stage hormone receptor positive breast cancer is typically treated with adjuvant
endocrine therapy in order to decrease risk of breast cancer recurrence and to improve
overall survival from the disease. Typical agents used for treatment include tamoxifen and
the aromatase inhibitors. In postmenopausal women, aromatase inhibitor therapy is
increasingly common because it is associated with fewer long-term serious toxicities
compared to tamoxifen. However, aromatase inhibitors cause arthralgias in 40-50% of
patients, which can influence adherence to therapy and can lead to treatment discontinuation
in a minority of cases. The mechanism underlying development of this toxicity remains
unclear, and predictors of who will develop these symptoms remain undefined. This
observational study is designed to collect patient-reported outcomes and serial serum
samples in order to investigate potential etiologies of this bothersome toxicity.