S9630, Medroxyprogesterone in Treating Women With Breast Cancer

DISEASE CHARACTERISTICS: * One of the following histologically proven diagnoses: * Primary invasive adenocarcinoma of the unilateral or bilateral breast * Stage I, IIA, or IIB (T1-3, N0-1, M0) * No recurrent invasive breast cancer * Ductal carcinoma in situ (DCIS) * Lobular carcinoma in situ (LCIS) with microinvasion * Paget's disease of the nipple * No sarcoma, lymphoma, or apocrine, adenocystic, or squamous cell cancer of the breast * Currently free of breast cancer (no evidence of disease) * No evidence of distant disease on chest x-ray or chest CT scan and mammogram of the opposite breast within the past year * Prior definitive local treatment of primary lesion (mastectomy or breast-sparing procedure with radiotherapy) and either axillary node or sentinel node biopsy * Surgical margins clear of both infiltrating carcinoma (any type) and DCIS * No gross or microscopically positive margins except: * Invasive cancer or DCIS at the focal margin treated with definitive radiotherapy * Gross or LCIS at the final margin * Biopsy requirement waived for DCIS or LCIS with minimal microinvasion * Patients with breast-sparing procedure must have received or be planning to receive radiotherapy at start of tamoxifen treatment * No endometrial simple or cystic hyperplasia, proliferative changes, complex (adenomatous) or atypical hyperplasia, or carcinoma * Patients must be planning one of the following: * Starting adjuvant tamoxifen for five years OR * Started tamoxifen within 28 days prior to study and planning to receive adjuvant tamoxifen for five years * Hormone receptor status: * Candidate for adjuvant tamoxifen therapy PATIENT CHARACTERISTICS: Age: * Adult Sex: * Female Menopausal status: * Postmenopausal defined as: * At least 1 year since last menstrual period * At least 2 months since bilateral oophorectomy prior to breast cancer diagnosis * 4-12 months since last menstrual period and FSH elevated to postmenopausal range * Postmenopausal estrogen therapy and 55 years of age or older Performance status: * Not specified Life expectancy: * Not specified Hematopoietic: * Not specified Hepatic: * Not specified Renal: * Not specified Other: * Fertile patients must use effective contraception during and for at least 2 months after study * No other malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer, carcinoma in situ of the cervix, or stage I or II cancer currently in complete remission * No concurrent nonmalignant-related illness that would preclude study PRIOR CONCURRENT THERAPY: Biologic therapy: * Not specified Chemotherapy: * Adjuvant chemotherapy allowed * No concurrent chemotherapy Endocrine therapy: * See Disease Characteristics * No prior hormonal treatment for breast cancer (except tamoxifen) * No concurrent postmenopausal estrogen therapy Radiotherapy: * See Disease Characteristics Surgery: * See Disease Characteristics * No prior or concurrent hysterectomy Other: * No prior or current participation in an adjuvant intergroup trial