Anastrozole and Letrozole After Surgery for the Treatment of Stage I-III Breast Cancer

PRIMARY OBJECTIVE: I. To estimate the proportion of women who have adequate estrone (E1) and estradiol (E2) suppression after 8-10 weeks of adjuvant anastrozole 10 mg once daily (ANA10) having had inadequate E1 and E2 suppression after 8-10 weeks of standard dose anastrozole 1 mg once daily (ANA1). SECONDARY OBJECTIVES: I. To estimate the proportion of women with elevated E1 and E2 levels after 8-10 weeks of adjuvant ANA1. II. To estimate the proportion of women with elevated E1 and E2 levels after 8-10 weeks of adjuvant ANA1 whose E1 and E2 levels remain elevated after 8-10 weeks of adjuvant ANA10. III. To examine the toxicity profile of ANA1 over the 8-10 weeks of treatment, ANA10 over the 8-10 weeks of treatment, and letrozole over the 8-10 weeks of treatment. IV. To examine concentrations of anastrozole at both the ANA1 and ANA10 dose levels. V. To examine E1 and E2 concentrations, as well as letrozole drug levels, in patients receiving letrozole (following ANA10). VI. To bank deoxyribonucleic acid (DNA) for examination of single-nucleotide polymorphism (SNP)-set(s) determined in the ongoing Mayo Clinic Breast Cancer Specialized Program of Research Excellence (SPORE) Project 4. EXPLORATORY OBJECTIVE: I. To examine association between clinical variables such as age, age at menopause, body mass index (BMI), receipt of chemotherapy, chemotherapy regimen, and dose on E1 and E2 levels after 8-10 weeks of ANA10. OUTLINE: Patients receive anastrozole orally (PO) once daily (QD) for 56-70 days (8-10 weeks). Patients with E1 \>= 1.3 pg/ml and E2 \>= 0.5 pg/ml continue to receive anastrozole PO QD for another 56-70 days (8-10 weeks). Patients then receive letrozole PO QD for 8-10 weeks. Treatment continues in the absence of disease progression or unacceptable toxicity.