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Five-Year Data from Austrian Trial Shows Significant Benefit in Switching From Tamoxifen to Anastrozole: Presented at SABCS

By Cameron Johnston

SAN ANTONIO, TX -- December 14, 2005 -- The 5-year results of the Austrian Breast Cancer Study Group trial 8 (ABCSG-8) show a significant benefit among women with breast cancer who take tamoxifen for 2 years and then switch to anastrozole.

The study involved 1454 patients who were randomized to receive tamoxifen for 5 years, or 1472 who received tamoxifen for 2 years followed by 3 years of anastrozole following surgery.

According to Raimund Jakesz, MD, professor of medicine, Vienna Medical School, Vienna, Austria, other trials have shown that efficacy is improved when a patient is switched from tamoxifen to an aromatase inhibitor such as letrozole, anastrozole, or exemestane.

However, no studies have shown that more benefit could be derived from switching part way though a course of tamoxifen to another agent, Dr. Jakesz said in a presentation here on December 9^th at the 28^th Annual San Antonio Breast Cancer Symposium (SABCS).

"Tamoxifen is no longer the optimal choice of adjuvant endocrine treatments," Dr. Jakesz said, adding that aromatase inhibitors are more powerful endocrine modifiers and therefore should be used as first-line therapy.

Women in the ABCSG-8 study all underwent mastectomy or breast-conserving surgery prior to drug treatment. Four of 5 were both estrogen and progesterone receptor-positive, and 19% were estrogen receptor-positive. They were not permitted to have chemotherapy.

Looking at the sequencing analysis (ie, the entire duration of the study), there were 180 events among 2926 patients over a mean follow-up time of 54.6 months. At the 2-year switch point there was no difference in event-free survival between groups (98.3% vs 8.0%).

However, by the end of the study, 94.4% of those who switched to anastrozole from tamoxifen were disease event-free compared with 92.9% of those who remained on tamoxifen who were event-free.

As for the postswitch analysis, which included 2529 women, there were 69 events among patients who remained on tamoxifen and 44 among those who switched to anastrozole. This represents a hazard ratio of 0.62 (P = .011) over a mean follow-up- of 31.1 months. There were 26 local and 68 distant metastases and 22 contralateral breast cancers. Event-free survival figures were 92.8% and 88.9% favoring the group that switched from tamoxifen to anastrozole versus the group that remained on tamoxifen.

Distant recurrence-free survival also favored patients who had switched from tamoxifen to anastrozole (95.9%) versus those who remained on tamoxifen (94.4%), with 41 events versus 28 events (HR 0.67, P = .095).

There were 34 bone fractures recorded in patients receiving anastrozole compared with 16 in the group taking tamoxifen. Endometrial cancer occurred in 7 patients on tamoxifen and 1 on anastrozole. Myocardial infarctions were recorded in 3 patients on anastrozole and in 2 patients on tamoxifen.

Dr. Jakesz said that switching from tamoxifen to anastrozole after 2 years reduced events by 39% (P = .01). The incidences of local and distant recurrence and contralateral disease were all reduced more or less equally.

Taking into account the first 2 years, when part of the cohort was on tamoxifen, the overall reduction in events was 24% in favor of those who switched to anastrozole, he said.

These findings are in line with what has been seen in other major trials using aromatase inhibitors, such as the BIG-98 trial, which used letrozole, and the Anastrozole Tamoxifen Alone or in Combination (ATAC) trial.

Trials using aromatase inhibitors from the outset after surgery are also needed to determine the best strategy for their use, Dr. Jakesz said.


[Presentation title: The Benefits of Sequencing Adjuvant Tamoxifen and Anastrozole in Postmenopausal Women With Hormone-Responsive Early Breast Cancer: 5 Year-Analysis of ABCSG Trial 8. Abstract 13]

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