Long-term superiority of anastrozole over tamoxifen confirmed in early breast cancer

December 14, 2007

Anastrozole has clear long-term superior efficacy over tamoxifen and the benefits of treatment with anastrozole are maintained long after treatment is completed, according to an Article in The Lancet Oncology to be published Online on Saturday December 15, 2007.

The study presents updated data from The Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial at 100-months of follow-up and "is the longest follow-up to date after 5 years of upfront treatment with aromatase inhibitors."

The ATAC trial compared the safety and efficacy of tamoxifen with the aromatase inhibitor anastrozole as well as the combination of both drugs given for 5 years to postmenopausal women with hormone-sensitive early breast cancer who were randomly assigned to the three treatment arms. Findings from a previous study at 68 months of follow-up (see Lancet 2005; 365: 60-62) showed that, compared with tamoxifen, hormone-receptor-positive patients assigned to anastrozole had increased disease-free survival (by about 15%), increased time to disease recurrence (by about 25%), less cancer spread (time to distant recurrence by 16%), and a lower number of new cancers in the other breast (by over 50%). In a further report at 68 months of follow-up (see Lancet Oncology 2006; 7: 633-43), anastrozole treatment was associated with significantly fewer serious adverse events than treatment with tamoxifen, including fewer occurrences of thromboembolism, ischaemic cerebrovascular events, and endometrial cancer, although an increased number of fractures was noted for patients on anastrozole.

As a result of findings from previous studies, aromatase inhibitors are now recommended as adjuvant treatment for postmenopausal women with hormone-receptor-positive early breast cancer. However, questions remain about whether these benefits and side-effects continue after treatment is completed.

The ATAC Trialists' Group therefore report Online in The Lancet Oncology long-term findings up to 4 years after treatment completion. The authors note that for disease-free survival, the previously reported benefit for the anastrozole group was maintained after treatment was completed. Furthermore, differences between groups in the time to recurrence increased over time (from 2.8% after 5 years to 4.8% after 9 years) and recurrence rates after treatment completion remained significantly lower for patients on anastrozole compared with patients on tamoxifen. According to the authors, this shows that treatment benefits of adjuvant treatment with anastrozole continue in the long-term, even after treatment is completed. The effect on distant recurrence was maintained, which is now statistically significant, but as in previous reports of the ATAC trial, there was still no difference between the two monotherapy groups in terms of overall survivalâ€"probably related in part to the large number of competing (non-breast cancer) causes of death as the patient population ages (mean age at this analysis was 72 years).

Further, there was no significant difference in risk of cardiovascular morbidity or mortality between the treatment groups, an area of concern that has been raised previously with the use of aromatase inhibitors. Importantly, the researchers noted that the increase in fracture rates previously seen in patients on anastrozole seem to be associated with active treatment, as during the post-treatment follow-up period, fracture rates for patients on anastrozole were now very similar to those of patients on tamoxifen.

The authors conclude: "The findings of this report extend the previously reported superior efficacy of anastrozole over tamoxifen at 68 months of follow-up to 100 months. We also show a carryover benefit for recurrence in the hormone-receptor-positive population which is larger than that previously shown for tamoxifen."
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The paper associated with this release can be found at http://www.eurekalert.org/jrnls/lance/TLOATACFINAL.pdf

Lancet

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