By Mary Wessling
ST. GALLEN, Switzerland -- March 17, 2009 -- Anastrazole appears to be significantly superior to tamoxifen in preventing disease recurrence, including distant recurrence, and contralateral breast cancer in patients with hormone-responsive early breast cancer, researchers stated here at the St. Gallen Oncology Conferences: Primary Therapy of Early Breast Cancer International Conference (SGBCC).
Anthony Howell, MD, Christie Hospital NHS Trust, Manchester, United Kingdom, presented the most recent analysis of the Anastrozole, Tamoxifen, Alone or in Combination (ATAC) trial on March 13 in a poster presentation.
The study compared women with hormone-responsive breast cancer who were randomised to treatment with anastrozole (n = 2,618) or tamoxifen (n = 2,598). Patients have been followed up for a median of 100 months, and the analysis presented shows data for years 2, 5, and 9.
At 9 years, the total number of all first events for anastrozole versus tamoxifen, with the Kaplan-Meier proportion estimate in parentheses, was 609 (25.8%) vs 694 (29.9%; hazard ratio [HR] = 0.85).
The number of recurrences was 385 (17.0%) vs 488 (21.8%; HR = 0.76). All distant recurrences were 303 (33.2%) vs 354 (15.7%; HR = 0.84). Contralateral primary cancers were 47 (2.5%) vs 78 (4.2%; HR = 0.58). The number of deaths following recurrences was 241 (10.8%) vs 266 (12.3%; HR = 0.89).
For years 0 to 9 since randomisation, the number of events prevented by anastrozole compared with tamoxifen was reported as follows: all first events, 85 (15%); recurrences, 103 (24%); all distant recurrences, 51 (16%); contralateral primary cancers, 31 (42%); and deaths following recurrences, 25 (11%).
During the 0 to 5 year treatment period, compared with tamoxifen, anastrozole was associated with fewer incidences of vaginal bleeding (152 [5.9%] vs 286 [11.1%]; 95% confidence interval [CI], 0.50 [0.41-0.62]); vaginal discharge (98 [3.8%] vs 343 [13.3%]; 95% CI, 0.26 [0.20-0.32]), and endometrial cancer (4 [0.2%] vs 12 [0.5%]; 95% CI, 0.33 [0.08-1.10]).
In years 0 to 5, anastrozole was also associated with fewer ischaemic cardiovascular events (145 [5.6%] vs 114 [4.4%]; 95% CI, 1.28 [0.99-1.67]), venous thrombotic events (82 [3.2%] vs 142 [5.5%]; 95% CI, 0.57 [0.43-0.76]), deep venous thromboembolic events (49 [1.9%] vs 79 [3.1%]; 95% CI, 0.61 [0.42-0.89]), and hot flushes (935 [36.1%] vs 1,078 [41.8%]; 95% CI, 0.79 [0.70-0.88]).
The predefined adverse events that increased in years 0 to 5 in the anastrozole group compared with the tamoxifen group included arthralgia (1,234 [47.6%] vs 979 [37.9%]; 95% CI, 1.49 [1.33-1.47]) and fractures (307 [11.9%] vs 204 [7.9%]; 95% CI, 1.57 [1.30-1.90]).
For the treatment and post-treatment periods, there was a lower prevalence of serious adverse events for anastrozole compared with tamoxifen, and the increased yearly fracture episode rate noted during treatment did not continue into the post-treatment follow-up period.
Greater reductions in recurrence and distant recurrence events were observed for the anastrozole group compared with the tamoxifen group in the 5-year treatment period and continued at 9 years. Distant recurrences closely reflect subsequent mortality rates from breast cancer.
Following completion of therapy, anastrozole conveyed a larger carryover effect with significantly reduced risk of recurrence events compared with tamoxifen.
The 100-month data showed that, in hormone-responsive breast cancer patients, anastrozole is well tolerated in the long term. The side-effect profile in this population was similar to the previously published population.
In postmenopausal women with hormone-responsive early breast cancer, the reduction in events with anastrozole versus tamoxifen observed in the mature data confirms the early data supporting the use of anastrozole as initial adjuvant therapy.
[Presentation title: Initial Adjuvant Therapy With Anastrozole - Early- and Late-Event Data From the Arimidex, Tamoxifen, Alone or in Combination (ATAC) Trial in The Hormone Responsive Population. Abstract 0130]
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