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Extended Adjuvant Exemestane Cuts Breast Cancer Relapse: Presented at SGOC

By Joanna Lyford

ST. GALLEN, SWITZERLAND -- March 19, 2007 -- Extended adjuvant therapy with exemestane reduces the risk of late breast cancer relapse in women who have completed 5 years of tamoxifen, according to results of a large clinical trial.

Results of the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-33 study corroborate growing evidence of the benefits of aromatase inhibitors in the extended adjuvant setting.

Lead investigator Charles Geyer, MD, director, breast medical oncology, Allegheny General Hospital, Pittsburgh, Pennsylvania, United States, presented the findings here at the 10^th International St. Gallen Oncology Conference: Primary Therapy of Early Breast Cancer (SGOC), held in St. Gallen, Switzerland.

The B-33 study randomised 1,598 postmenopausal women to either exemestane or placebo. All participants had hormone-responsive tumours and were disease-free after undergoing 5 years of tamoxifen therapy.

"The majority of patients are disease-free at the time of tamoxifen discontinuation but recurrences continue to occur over prolonged periods of time," Dr. Geyer explained. "Over half of recurrences and over two thirds of deaths occur after the first 5 years of follow-up."

Accrual into the B-33 study stopped in October 2003 after disclosure of results from the MA-17 trial (Adjuvant Letrozole [Femara] vs Placebo in Women With Primary Breast Cancer Completing 5 Years of Tamoxifen). This landmark study was the first to demonstrate the benefit of extended therapy with the aromatase inhibitor letrozole in postmenopausal women after standard adjuvant tamoxifen.

Since the MA-17 results changed the standard of care, the B-33 data monitoring committee decided to unblind the study and offer exemestane to women in the placebo group. Forty-four percent of patients chose to crossover to exemestane and the results presented here are an intent-to-treat analysis with 30 months of follow-up.

Exemestane was associated with a significant improvement in relapse-free survival compared with placebo. The hazard ratio (HR) was 0.44, indicating a 56% reduction in breast cancer relapses (P = .004).

Extended adjuvant therapy resulted in improved disease-free survival (DFS) versus placebo (HR 0.69), although this only achieved borderline statistical significance (P = .07).

At 30 months of follow-up, exemestane and placebo arms did not show significant differences in overall survival (HR 1.20, P = .63) or distant DFS (HR 0.69, P = .13).

Importantly, toxicity in the exemestane treatment arm was acceptable in the adjuvant setting, according to the study authors. Up to the time of unblinding there was 1% grade 4 toxicity in each group and no treatment-related deaths. The most common grade 3 or 4 toxicities in the exemestane and placebo groups were arthralgia (1.0% vs 0.5%), fatigue (0.9% vs 0.5%), and bone pain (0.5% vs 0.7%).

There were no differences between the groups in bone fractures or quality-of-life measures, including vasomotor, psychosocial, physical, or sexual symptoms.

"Despite the premature [study] closure and crossover to exemestane, original exemestane assignment resulted in borderline improvement in DFS and significant improvement in DFS of a similar magnitude to that seen in MA-17," Dr. Geyer et al conclude.


[Presentation title: Exemestane (EXE) as Extended Adjuvant Therapy After 5 Years of Tamoxifen (TAM): Results of NSABP B-33. Abstract P117]

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