Letrozole vs Placebo in Postmenopausal Women with Primary Breast Cancer After Adjuvant Aromatase Inhibitor Therapy

Study start date: August 24, 1998

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed primary invasive breast carcinoma resected at time of original diagnosis * No ductal carcinoma in situ * Axillary lymph node negative, positive, or unknown * No evidence of metastases * No localized or distant breast cancer recurrence * Not registered on protocol NCCTG-893052, any other IBCSG protocol, or protocol SWOG-S9623 * Hormone receptor status: * Estrogen or progesterone receptor positive as defined by tumor receptor content at least 10 fmol/mg protein or receptor positive by ERICA or PgRICA * Unknown status allowed if effort to determine status has been made by immunocytochemistry * No contralateral breast cancer PATIENT CHARACTERISTICS: Age: * Postmenopausal Sex: * Female Menopausal status: * Postmenopausal defined by one of the following: * Age 50 or over at start of adjuvant tamoxifen * Under age 50 and considered postmenopausal by treating physician at start of adjuvant tamoxifen * Under age 50 at start of adjuvant tamoxifen and had bilateral oophorectomy (surgical or radiation) * Under age 50 and premenopausal at start of adjuvant tamoxifen, but became amenorrheic during tamoxifen and remained amenorrheic for at least 1 year * Considered postmenopausal by physician with LH/FSH levels under the treatment center's postmenopausal limits Performance status: * ECOG 0-2 Life expectancy: * At least 5 years Hematopoietic: * WBC ≥ 3,000/mm\^3 OR * Granulocyte count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 Hepatic: * AST and/or ALT \< 2 times upper limit of normal (ULN) (unless imaging examinations have ruled out metastatic disease) * Alkaline phosphatase \< 2 times ULN (unless imaging examinations have ruled out metastatic disease) Renal: * Not specified Other: * No concurrent medical or psychiatric condition that would preclude study participation * No other malignancy within the past 5 years except adequately treated superficial squamous cell or basal cell skin cancer or carcinoma in situ of the cervix * Able to swallow study drug * Adequate oral intake PRIOR CONCURRENT THERAPY: Biologic therapy: * Not specified Chemotherapy: * Prior adjuvant chemotherapy allowed * No concurrent chemotherapy Endocrine therapy: * Completed at least 4.5 but no more than 6 years of adjuvant tamoxifen after resection * Completed at least 4.5-6 years of adjuvant aromatase inhibitor as initial therapy or after tamoxifen * No more than 3 months since prior adjuvant tamoxifen * No concurrent hormone replacement therapy (e.g., megestrol) * No concurrent selective estrogen-receptor modulators (e.g., raloxifene or idoxifene) * Concurrent intermittent vaginal estrogens (e.g., Estring) allowed if other local measures for intractable vaginal atrophy are insufficient * No other concurrent aromatase inhibitors * No more than 2 years since prior aromatase inhibitor therapy (re-randomization) Radiotherapy: * Prior radiotherapy allowed Surgery: * See Disease Characteristics Other: * At least 1 month since prior investigational drugs * Prior treatment on a clinical trial for breast cancer allowed if permission has been obtained from the sponsors of the original study for their patient to participate on MA.17/JMA.17/BIG-97-01 * No prior placebo on core protocol * No concurrent anticancer therapy * Concurrent thyroid medication, calcium, vitamin D, and bisphosphonates allowed