Low-dose Oral Cyclophosphamide and Methotrexate Maintenance for Hormone Receptor-negative Early Breast Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed stage I, II, or III breast cancer * T1-3, N0-2, M0 * Patients with sentinel node biopsy positive disease must have undergone axillary dissection * Tumor must be confined to the breast without detected metastases elsewhere * T4 disease with minimal dermal invasion allowed * No T4 disease with ulceration of skin, infiltration of skin (except pathologically minimal dermal involvement), peau d'orange, or inflammatory breast cancer * No bilateral breast cancer (except in situ carcinoma) or suspicious mass in opposite breast that has not been proven benign * No distant metastases * No skeletal pain of unknown cause, elevated alkaline phosphatase, or bone scan showing hot spots that cannot be ruled out as metastases by x-ray, MRI, and/or CT * Must have undergone prior total mastectomy OR breast-conserving procedure (e.g., lumpectomy, quadrantectomy, or partial mastectomy with negative margins) with radiotherapy planned * Patients must begin or have begun an approved induction chemotherapy regimen within 8 weeks after definitive surgery * Negative surgical margins * Axillary clearance with at least 6 lymph nodes examined OR negative sentinel node biopsy * Known HER2 status by immunohistochemistry or fluorescence in situ hybridization * Hormone receptor status: * Estrogen and progesterone receptor negative * Less than 10% positive tumor cells by immunohistochemistry PATIENT CHARACTERISTICS: Age: * Not specified Sex: * Not specified Menopausal status: * Premenopausal, defined as less than 6 months since last menstrual period (LMP) AND no prior bilateral ovariectomy AND not on estrogen replacement (OR under age 50) OR * Postmenopausal, defined as prior bilateral ovariectomy OR more than 12 months since LMP without prior hysterectomy (OR age 50 and over) Performance status: * Not specified Life expectancy: * Not specified Hematopoietic: * WBC greater than 3,000/mm3 * Platelet count greater than 100,000/mm3 Hepatic: * See Disease Characteristics * Bilirubin less than 2.0 mg/dL * ALT less than 1.5 times upper limit of normal OR AST less than 60 IU/L Renal: * Creatinine less than 1.2 mg/dL Other: * Not pregnant or lactating within the past 6 months * Fertile patients must use effective barrier contraception * No other prior or concurrent malignancy except adequately treated basal or squamous cell carcinoma of the skin, carcinoma in situ of the cervix, or contralateral or ipsilateral in situ breast carcinoma * No psychiatric or addictive disorders that would preclude study * No non-malignant systemic disease that would preclude study PRIOR CONCURRENT THERAPY: Biologic therapy: * Prior trastuzumab (Herceptin) allowed Chemotherapy: * See Disease Characteristics * No prior adjuvant or neoadjuvant chemotherapy for breast cancer Endocrine therapy: * No prior endocrine therapy for breast cancer or prevention * No prior tamoxifen or raloxifene for breast cancer Radiotherapy: * No prior radiotherapy for breast cancer except primary irradiation Surgery: * See Disease Characteristics Other: * No prior preventative therapy for breast cancer