Musculoskeletal Pain and the Prevalence of Rheumatoid Arthritis in Breast Cancer Patients During Cancer Treatment: A Retrospective Study

PURPOSE: Breast cancer patients often develop musculoskeletal pain, resembling that experienced by patients with rheumatoid arthritis (RA), during cancer treatment. This study aimed to investigate the causes of musculoskeletal pain, including RA, among breast cancer patients. METHODS: This retrospective study included breast cancer patients experiencing new-onset arthralgia during cancer treatment along with age- and sex-matched controls without breast cancer, who were evaluated at the Rheumatologic clinic between 2004 and 2017. The causes of musculoskeletal pain were compared between breast cancer patients and controls. The effects of cancer treatment on arthralgia and factors associated with RA were examined. RESULTS: A total of 146 breast cancer patients and 102 controls were included in the final analysis. The most common cause of arthralgia during breast cancer treatment was osteoarthritis (OA, 61.0%), followed by enthesopathy/tendinopathy (28.1%), which included tendinitis, adhesive capsulitis, and carpal tunnel syndrome. Overall, 50.0% of 72 breast cancer patients receiving aromatase inhibitors (AIs) satisfied the criteria of AI-induced musculoskeletal symptoms (AIMSS). The mean symptom duration (i.e., the time between pain onset and evaluation by a rheumatologist) was shorter in breast cancer patients than in controls (7.0 ± 12.1 vs. 14.8 ± 24.9 months, respectively; p = 0.004). RA was diagnosed in 3 (2.1%) breast cancer patients and 3 (2.9%) controls. All breast cancer patients with RA had an elevated erythrocyte sedimentation rate (ESR, 66.7 ± 25.0 mm/h), whereas those without RA had a normal ESR (20.4 ± 21.5 mm/h). Patients with breast cancer required more analgesics than the controls. CONCLUSION: OA and enthesopathy/tendinopathy are the most common causes of arthralgia in breast cancer patients, which may concurrently manifest as AIMSS. Patients with breast cancer did not have a higher prevalence of RA than those without breast cancer.