ABSTRACT
BACKGROUND: Although anastrozole (ANA), an aromatase inhibitor (AI), has been widely used for breast cancer patients; adverse events during ANA therapy in Japanese patients have not been reported. METHODS: The study included 656 postmenopausal breast cancer patients receiving ANA as postoperative adjuvant therapy in our hospital. Adverse events during ANA therapy, such as musculoskeletal effects and cerebro- and cardiovascular accidents, were investigated over a 5-year period. The percentage changes in lumbar (L2-4) spine bone mineral density (BMD) were determined in 71 patients receiving ANA alone and 26 patients receiving bisphosphonate in combination with ANA for 7-24 months. RESULTS: The follow-up period ranged from 6 to 60 months (median 23 months). Joint pain, the most common adverse event, was observed in 3.6% (24/656) of the patients. Cerebral infarctions occurred in 0.3% (2/656) of the patients, and no cardiovascular accidents occurred. Bone fractures occurred in nine patients receiving ANA alone. The mean age and BMD of the nine patients were 67.6 years and 71.8% (compared to the young adult mean BMD), respectively. Accumulated and annual fracture rates were 1.3 and 0.8%, respectively. A decrease in BMD was observed in 62.0% (44/71) of the ANA group compared to 26.9% (7/26) of the combination bisphosphonate group (P < 0.01). CONCLUSION: Incidence of adverse events during AI therapy in this Japanese postmenopausal population appears to be lower than that of the ATAC trial. The incidence of bone fractures during AI therapy is lower in Japan, and the addition of bisphosphonates enhances bone health. We should perform a prospective trial in the future to investigate the precise risk of bone fractures in Japanese patients.