Background: A randomized, double-blind, multicenter study was conducted to compare the anti-tumor activity of letrozole vs. tamoxifen in postmenopausal women with ER and/or PgR positive primary untreated breast cancer.
Patients and methods: Three hundred thirty-seven postmenopausal women with ER and/or PgR positive primary untreated breast cancer were randomly assigned once daily treatment with either letrozole 2.5 mg or tamoxifen 20 mg for four months. At baseline none of the patients were considered to be candidates for breast-conserving surgery (BCS) and 14% of the patients were considered inoperable. The primary endpoint was to compare overall objective response (CR + PR) determined by clinical palpation. Secondary endpoints included overall objective response on ultrasound and mammography and the number of patients who qualified for BCS.
Results: Overall objective response rate (clinical palpation) was statistically significantly superior in the letrozole group, 55% compared to tamoxifen, 36% (P < 0.001). Secondary endpoints of ultrasound response, 35% vs. 25% (P = 0.042), mammographic response, 34% vs. 16% (P < 0.001), and BCS, 45% vs. 35% (P = 0.022) between the letrozole and tamoxifen groups, respectively, showed letrozole to be significantly superior. Both treatments were well tolerated.
Conclusions: This study shows that letrozole is more effective than tamoxifen as preoperative therapy in postmenopausal patients with ER and/or PgR positive primary untreated breast cancer and is at least as well tolerated.