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, Jong-Hyeon Jeong, D Lawrence Wickerham, Roy E Smith, Patricia A Ganz, Stephanie R Land, Andrea Eisen, Louis Fehrenbacher, William B Farrar, James N Atkins, Eduardo R Pajon, Victor G Vogel, Joan F Kroener, Laura F Hutchins, André Robidoux, James L Hoehn, James N Ingle, Charles E Geyer, Joseph P Costantino, Norman Wolmark
Journal of Clinical Oncology: Official Journal of the American Society of Clinical Oncology 2008 April 20, 26 (12): 1965-71

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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