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Randomized Controlled Trial
. 2008 Apr 20;26(12):1965-71.
doi: 10.1200/JCO.2007.14.0228. Epub 2008 Mar 10.

Benefit From Exemestane as Extended Adjuvant Therapy After 5 Years of Adjuvant Tamoxifen: Intention-To-Treat Analysis of the National Surgical Adjuvant Breast And Bowel Project B-33 Trial

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Randomized Controlled Trial

Benefit From Exemestane as Extended Adjuvant Therapy After 5 Years of Adjuvant Tamoxifen: Intention-To-Treat Analysis of the National Surgical Adjuvant Breast And Bowel Project B-33 Trial

Eleftherios P Mamounas et al. J Clin Oncol. .

Abstract

Purpose: Patients with early-stage, hormone receptor-positive breast cancer have considerable residual risk for recurrence after completing 5 years of adjuvant tamoxifen. In May 2001, the National Surgical Adjuvant Breast and Bowel Project (NSABP) initiated accrual to a randomized, placebo-controlled, double-blind clinical trial to evaluate the steroidal aromatase inhibitor exemestane as extended adjuvant therapy in this setting.

Patients and methods: Postmenopausal patients with clinical T(1-3)N(1)M(0) breast cancer who were disease free after 5 years of tamoxifen were randomly assigned to 5 years of exemestane (25 mg/d orally) or 5 years of placebo. Our primary aim was to test whether exemestane prolongs disease-free survival (DFS). In October 2003, results of National Cancer Institute of Canada (NCIC) MA.17 showing benefit from adjuvant letrozole in this setting necessitated termination of accrual to B-33, unblinding, and offering of exemestane to patients in the placebo group.

Results: At the time of unblinding, 1,598 patients had been randomly assigned; 72% in the exemestane group continued on exemestane and 44% in the placebo group elected to receive exemestane. With 30 months of median follow-up, original exemestane assignment resulted in a borderline statistically significant improvement in 4-year DFS (91% v 89%; relative risk [RR] = 0.68; P = .07) and in a statistically significant improvement in 4-year relapse-free survival (RFS; 96% v 94%; RR = 0.44; P = .004). Toxicity, assessed up to time of unblinding, was acceptable for the adjuvant setting.

Conclusion: Despite premature closure and crossover to exemestane by a substantial proportion of patients, original exemestane assignment resulted in non-statistically significant improvement in DFS and in statistically significant improvement in RFS.

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