Adverse reactions listed as follows are classified according to frequency and System Organ Class (SOC). Frequency groupings are defined according to the following convention: very common (≥ 1/10), common (≥ 1/100 to < 1/10), uncommon (≥ 1/1,000 to < 1/100), rare (≥ 1/10,000 to <1/1,000), and very rare (<1/10,000). The most frequently reported adverse reactions were headache, hot flushes, nausea, rash, arthralgia, joint stiffness, arthritis, and asthenia. (See Table 3.)

The table as follows presents the frequency of pre-specified adverse events in the ATAC study after a median follow-up of 68 months, irrespective of causality, reported in patients receiving trial therapy and up to 14 days after cessation of trial therapy. (See Table 4.)

Fracture rates of 22 per 1,000 patient-years and 15 per 1,000 patient-years were observed for the anastrozole tablets and tamoxifen groups, respectively, after a median follow-up of 68 months. The observed fracture rate for anastrozole tablets is similar to the range reported in age-matched postmenopausal populations. The incidence of osteoporosis was 10.5% in patients treated with anastrozole tablets and 7.3% in patients treated with tamoxifen.
It has not been determined whether the rates of fracture and osteoporosis seen in ATAC in patients on anastrozole tablets treatment reflect a protective effect of tamoxifen, a specific effect of anastrozole tablets, or both.
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