There were no clear efficacy differences observed between tamoxifen and anastrozole for the prevention of locoregional and contralateral breast cancer in postmenopausal women with locally excised ductal carcinoma in situ (DCIS), a new study published online ahead of print in the journal The Lancet has shown.1
Although third-generation aromatase inhibitors are more effective than tamoxifen for preventing recurrence in postmenopausal women with hormone receptor-positive invasive breast cancer, there is limited evidence demonstrating whether anastrozole is more effective than tamoxifen for postmenopausal women with hormone receptor-positive DCIS. Therefore, researchers sought to evaluate the efficacy of anastrozole compared with tamoxifen in those patients.
For the multicenter, double-blind, placebo-controlled trial, researchers enrolled 2980 postmenopausal women with locally excised, hormone receptor-positive DCIS. Participants were randomly assigned 1:1 to receive anastrozole 1 mg orally or tamoxifen 20 mg orally daily for 5 years.
Results showed that at a median follow-up of 7.2 years, there were 67 recurrences for anastrozole and 77 recurrences for tamoxifen (HR, 0.89; 95% CI, 0.64 – 1.23). Researchers found that anastrozole was non-inferior, but not superior to tamoxifen (P = .49).
In regard to safety, fractures, musculoskeletal events, hypercholesterolemia, and strokes were more frequent with anastrozole, while muscle spasms, gynecological cancers and symptoms, vasomotor symptoms, and deep vein thromboses were more common with tamoxifen.
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The findings suggest that anastrozole is another treatment option for postmenopausal women with hormone receptor-positive DCIS and may be more appropriate from some women when contraindications for tamoxifen are present.
The investigators noted that longer follow-up is necessary to fully assess differences in treatment outcomes.
- Forbes JF, Sestak I, Howell A, et al. Anastrozole versus tamoxifen for the prevention of locoregional and contralateral breast cancer in postmenopausal women with locally excised ductal carcinoma in situ (IBIS-II DCIS): a double-blind, randomised controlled trial [published online ahead of print on December 11, 2015]. Lancet. doi: 10.1016/S0140-6736(15)01129-0.