DISEASE CHARACTERISTICS: Histologically proven adenocarcinoma of the breast that is potentially curable Prior treatment with one of the following therapies required: Segmental mastectomy (lumpectomy) followed by radiotherapy Chest wall irradiation allowed only in patients with T4 dermal involvement on pathologic diagnosis Further excision or boost radiotherapy to the tumor bed recommended if microscopic disease found at mastectomy margins Total mastectomy Chest wall irradiation required if microscopic disease found at mastectomy margins Clinical stage T1-3a N0-2 M0 disease prior to surgery The following T4 features exclude: Chest wall extension Edema (including peau d'orange) Skin ulceration Satellite skin nodules confined to same breast Inflammatory carcinoma Pathologic stage T1-4 NX-2 M0 disease following surgery Eligible T4 tumors are those with dermal involvement on pathology assessment only Pathologic assessment of axillary lymph nodes required May be omitted in patients with clinical N0 status provided other entry criteria are met No bilateral breast cancer without complete resection of both sides Hormone receptor status: Estrogen and progesterone receptor status determined from primary tumor when possible by quantitative biochemical methods or immunohistochemistry Results recorded as positive or negative if immunohistochemistry used Unknown status does not exclude provided other entry criteria are met