Inclusion Criteria

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