New data presented at the recent San Antonio Breast Cancer Symposium demonstrated that anastrozole(Drug information on anastrozole) (Arimidex), as an adjuvant treatment in postmenopausal women with early breast cancer, significantly reduced disease recurrence. After a median follow-up of 33.3 months and a median duration of treatment of 30.7 months, 317 of 3,125 women in the anastrozole group relapsed or died, compared with 379 of 3,116 women in the tamoxifen(Drug information on tamoxifen) (Nolvadex) group (P = .0129). This represents a 17% reduction in the risk of disease recurrence with anastrozole treatment. Among women in the anastrozole group with confirmed hormone-sensitive tumors, the reduction in risk of recurrence was 22% compared to the tamoxifen group (P = .0054).
The new data are the first results from the ATAC (Arimidex, Tamoxifen Alone or in Combination) study. The principal US investigator, Aman Buzdar, MD, of The University of Texas M. D. Anderson Cancer Center in Houston, said the outcome was important for postmenopausal women with early breast cancer. "Now after 20 years, tamoxifen’s established benefits in early breast cancer are being challenged," he said. "Tamoxifen is a very effective drug, but it has side effects, like an increased risk of endometrial cancer, that have to be managed. The goal of research in this area is to improve that profile."
Trial Design
The multicenter, randomized, double-blind study involved 9,366 patients from 380 cancer centers in 21 countries. Enrollees consisted of early breast cancer patients who had completed primary surgery and chemotherapy (if given) and were candidates for adjuvant hormonal therapy. The trial was designed to determine if anastrozole is equal to, or more effective than, tamoxifen, and whether anastrozole offers additional safety and tolerability benefits. The study also included a combination treatment arm (tamoxifen plus anastrozole) to determine whether taking both medications together was better than taking tamoxifen alone.
Participants were randomized to receive anastrozole (1 mg daily), tamoxifen (20 mg daily), or a combination of the two agents for 5 years or until disease recurrence. Primary end points were disease-free survival and safety. Secondary end points were time to distant recurrence and survival. No additional benefit was seen with the combination arm over tamoxifen alone. In the combination group, 383 of 3,125 women relapsed or died, compared to 379 of 3,116 of women in the tamoxifen group.
Adverse Effects Contrasted
Anastrozole was associated with significantly fewer reports of endometrial cancer, thromboembolic events, and vaginal bleeding than tamoxifen. In terms of adverse events, deep-vein thrombosis was reported in 1.7% of the patients taking tamoxifen compared to 1.0% of the anastrozole recipients. Endometrial cancer occurred at a rate of 0.5% with tamoxifen compared to 0.1% with anastrozole. Vaginal bleeding was reported in 8.1% of tamoxifen patients and 4.5 % of anastrozole patients. Hot flashes (39.7% vs 34.3%) and weight gain (11.0% vs 9.2%) were also more common among women treated with tamoxifen, compared to those taking anastrozole.
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