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Letrozole as adjuvant endocrine therapy in postmenopausal women with breast cancer

The third-generation aromatase inhibitor letrozole offers a promising approach to treating hormone-sensitive breast cancer for postmenopausal women, through potent and specific inhibition of estrogen synthesis. In neoadjuvant and first-line treatment, letrozole demonstrated superior efficacy compared with tamoxifen in randomized Phase III trials. Initial results of Breast InterGroup 1–98, a large ongoing randomized trial investigating primary adjuvant endocrine treatment with either letrozole or tamoxifen, have recently been presented. Patients treated with letrozole demonstrated a 19% improvement in disease-free survival and a significant reduced risk of distant recurrences, holding out the prospect of a survival advantage over tamoxifen treatment with further maturation of the trial. For patients who have already completed 5 years of tamoxifen, extended endocrine therapy with letrozole is a new therapeutic option based on the results of the MA-17 trial. The optimal use of aromatase inhibitors remains an open question, at least until results from randomized trials (BIG 1–98, TEAM) investigating the sequential use of an aromatase inhibitor and tamoxifen in comparison with continuous monotherapy become available.