Letrozole, a new oral aromatase inhibitor for advanced breast cancer: double-blind randomized trial showing a dose effect and improved efficacy and tolerability compared with megestrol acetate.

TLDR

The study compared two doses of letrozole with megestrol acetate as second‑line therapy in postmenopausal women with advanced breast cancer previously treated with antiestrogens. Five hundred fifty‑one patients were randomized in a double‑blind, multicenter trial to receive letrozole 2.5 mg, letrozole 0.5 mg, or megestrol acetate 160 mg daily, with tumor response, safety, and survival assessed up to 33 months and 45 months, respectively. Letrozole 2.5 mg produced a higher overall objective response rate (24% vs 16% with MA and 13% with 0.5 mg), longer response duration, superior time to treatment failure, improved overall survival, and better tolerability compared with both MA and the lower dose.

Abstract

PURPOSE To compare two doses of letrozole and megestrol acetate (MA) as second-line therapy in postmenopausal women with advanced breast cancer previously treated with antiestrogens. PATIENTS AND METHODS Five hundred fifty-one patients with locally advanced, locoregionally recurrent or metastatic breast cancer were randomly assigned to receive letrozole 2.5 mg (n = 174), letrozole 0.5 mg (n = 188), or MA 160 mg (n = 189) once daily in a double-blind, multicenter trial. Data were analyzed for tumor response and safety variables up to 33 months of follow-up evaluation and for survival up to 45 months. RESULTS Letrozole 2.5 mg produced a significantly higher overall objective response rate (24%) compared with MA (16%; logistic regression, P = .04) or letrozole 0.5 mg (13%; P = .004). Duration of objective response was significantly longer for letrozole 2.5 mg compared with MA (Cox regression, P = .02). Letrozole 2.5 mg was significantly superior to MA and letrozole 0.5 mg in time to treatment failure (P = .04 and P = .002, respectively). For time to progression, letrozole 2.5 mg was superior to letrozole 0.5 mg (P = .02), but not to MA (P = .07). There was a significant dose effect in overall survival in favor of letrozole 2.5 mg (P = .03) compared with letrozole 0.5 mg. Letrozole was significantly better tolerated than MA with respect to serious adverse experiences, discontinuation due to poor tolerability, cardiovascular side effects, and weight gain. CONCLUSION The data show letrozole 2.5 mg once daily to be more effective and better tolerated than MA in the treatment of postmenopausal women with advanced breast cancer previously treated with antiestrogens.