DISEASE CHARACTERISTICS:

• Histologically proven operable adenocarcinoma of the breast*

  • Stage I-IIIC disease

    • T1-4 (tumor size ≥ 1 cm), N0, M0 OR
    • T1-4, N1-3, M0 NOTE: *Bilateral, synchronous breast cancer allowed provided 1 primary tumor meets the staging criteria

• Must have undergone 1 of the following within the past 12 weeks:

  • Modified radical mastectomy

    • No evidence of gross or microscopic invasive tumor at the surgical resection margins

      • Close margins (tumor less than 1 mm from margin) allowed

  • Lumpectomy (clear margins preferred)

    • Ductal carcinoma in situ or lobular carcinoma in situ at the surgical resection margin allowed
    • No invasive tumor at the final resection margin

• Any number of previously excised nodes allowed

  • Axillary node dissection not required

• HER2/neu positive, negative, or unknown

  • Patients with HER2 positive tumors by immunohistochemistry 3+ staining or that demonstrate gene amplification by fluorescence in situ hybridization are eligible to receive trastuzumab (Herceptin) on study

• Hormone receptor status:

  • Not specified

PATIENT CHARACTERISTICS:

Age:

• 65 and over

Sex:

• Female

Menopausal status:

• Postmenopausal

Performance status:

• 0-2

Life expectancy:

• More than 5 years

Hematopoietic:

• Granulocyte count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3

Hepatic:

• Bilirubin no greater than upper limit of normal

Renal:

• Creatinine clearance at least 30 mL/min

Cardiovascular:

• No uncontrolled cardiac disease that would preclude study entry
• Left ventricular ejection fraction at least lower limit of normal (arm I, group B only)

Other:

• HIV negative

• No other concurrent active malignancy except nonmelanoma skin cancer

  • Disease considered not currently active if completely treated with less than a 30% risk of relapse
• No psychiatric illness that would preclude informed consent
• No other medical condition (e.g., uncontrolled infection) that would preclude study entry
• No hypersensitivity to fluorouracil
• No known dihydropyrimidine dehydrogenase deficiency

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• No prior chemotherapy for breast cancer
• No other concurrent chemotherapy

Endocrine therapy:

• Up to 4 weeks of prior tamoxifen for current breast cancer allowed
• Prior tamoxifen or raloxifene for chemoprevention (e.g., breast cancer prevention study) or other indications (including prior breast cancer) allowed but must be discontinued before study entry
• No concurrent hormonal therapy except steroids for adrenal failure, hormones for non-disease related conditions (e.g., insulin for diabetes), or intermittent dexamethasone as an antiemetic

Radiotherapy:

• Not specified

Surgery:

• See Disease Characteristics

Other:

• No concurrent dexrazoxane
• No concurrent bisphosphonates except for treatment of osteoporosis