Letrozole After Tamoxifen in Treating Women With Breast Cancer

RATIONALE: Estrogen can stimulate the growth of breast cancer cells. Hormone therapy using letrozole may fight breast cancer by reducing the production of estrogen. PURPOSE: This randomized phase III trial is studying letrozole to see how well it works in treating women with breast cancer who have received tamoxifen for at least 5 years.

OBJECTIVES: Primary * Compare the disease-free survival and overall survival of postmenopausal women with primary breast cancer who have completed at least five years of adjuvant aromatase inhibitor as initial therapy or after tamoxifen treated with letrozole or placebo. Secondary * Compare the incidence of contralateral breast cancer in patients treated with these regimens. * Evaluate the long-term clinical and laboratory safety of letrozole, in terms of lipid profile, cardiovascular morbidity and mortality, incidence of bone fractures, change in bone density, and common toxic effects, in this patient population. * Compare the quality of life of patients treated with these regimens. Re-randomization Primary * Compare disease-free survival of patients who, after receiving at least 4.5 years of letrozole, are re-randomized to receive an additional 5 years of letrozole vs placebo. Secondary * Determine whether common genetic polymorphisms for genes encoding proteins involved in pharmacokinetic and/or pharmacodynamic pathways for letrozole contribute to individual variation in toxicity and efficacy of letrozole therapy. OUTLINE: This is a randomized, double-blind, placebo-controlled, multicenter study. Patients are stratified according to receptor status (positive vs unknown), lymph node status (negative vs positive vs unknown), prior adjuvant chemotherapy (yes vs no), interval between last dose of aromatase inhibitor therapy and randomization (\< 6 months vs 6 months-2 years), and duration of prior tamoxifen use (0 years vs \< 2 years vs 2-4.5 years vs \> 4.5 years). Patients are randomized to 1 of 2 treatment arms. * Arm I: Patients receive oral letrozole once daily. * Arm II: Patients receive oral placebo once daily. In both arms, treatment continues for 5 years in the absence of disease progression or unacceptable toxicity. Patients in arm II may then be offered oral letrozole once daily for up to 5 years. Quality of life is assessed at baseline, at 6 months, and then annually for 4.5 years. * Double-blind, re-randomization: Patients who complete ≥ 4.5 years of letrozole (arm I) and who did not experience recurrent disease or new primary breast cancer, including ductal carcinoma in situ, may participate in the double-blind, placebo-controlled, re-randomization portion of the study. Patients are stratified according to lymph node status at enrollment (negative vs positive vs unknown), prior adjuvant chemotherapy (yes vs no), and interval between last dose of letrozole and re-randomization (\<6 months vs 6 months to 2 years). Common genetic single nucleotide polymorphisms for genes encoding proteins involved in pharmacokinetic and/or pharmacodynamic pathways for letrozole are analyzed in order to determine if these single nucleotide polymorphisms contribute to individual variation in toxicity and efficacy of letrozole therapy. Quality of life is assessed as during the first randomization. Patients are followed annually. PROJECTED ACCRUAL: A total of 4,700 patients will be accrued for this study.