Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed invasive breast cancer

- Stage I or II (T1, N0; T1, N1; T2, N0; or T2, N1)

- Unifocal disease (single focus that can be encompassed by one lumpectomy)

- The following histologies are eligilble:

- Invasive ductal

- Medullary

- Papillary

- Colloid (mucinous)

- Tubular

- No invasive or extensive in situ lobular carcinoma or pure ductal carcinoma in situ
(DCIS)

- No nonepithelial breast malignancies such as sarcoma or lymphoma

- Previously treated with lumpectomy of a lesion no greater than 3 cm and axillary
dissection of at least 6 lymph nodes or a sentinel node biopsy

- Six surgical clips in place delineating the margins of the tylectomy cavity

- Negative, inked histologic margins of lumpectomy (greater than 2 mm) OR
re-excision specimen available for confirmation

- Negative mammography post-lumpectomy or post-excision if malignancy-associated
microcalcifications were initially present

- No prior lumpectomy so extensive that the cosmetic result is low or poor prior
to radiotherapy

- No more than 3 positive axillary nodes

- No proven multicentric carcinoma (tumors in different quadrants of the breast or
tumor separated by at least 4 cm) with other clinically or radiographically
suspicious areas in the ipsilateral breast unless negative by biopsy

- No palpable or radiographically suspicious contralateral axillary, supraclavicular,
infraclavicular, or internal mammary nodes unless nodes are histologically negative

- No extensive intraductal carcinoma, indicated by one of the following according to
the Harvard definition:

- More than 25 % of invasive tumor is DCIS and DCIS is in adjacent breast tissue

- Intraductal carcinoma with microinvasion

- No previously treated contralateral breast cancer or synchronous ipsilateral breast
cancer

- No evidence of suspicious microcalcifications

- No Paget's disease of the nipple

- No skin involvement by disease, regardless of tumor size

- No distant metastases

- Hormone receptor status:

- Not specified

PATIENT CHARACTERISTICS:

Age

- 18 and over

Sex

- Female

Menopausal status

- Not specified

Performance status

- Not specified

Life expectancy

- At least 2 years

Hematopoietic

- Not specified

Hepatic

- Not specified

Renal

- Not specified

Other

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

- Technically suitable for breast radiotherapy

- No collagenous diseases (e.g., systemic lupus erythematosus, scleroderma, or
dermatomyositis)

- No other medical condition that would limit life expectancy

- No psychiatric or addictive disorders that would preclude giving informed consent

- No other malignancy within the past 5 years except nonmelanoma skin cancer

PRIOR CONCURRENT THERAPY:

Biologic therapy

- Not specified

Chemotherapy

- At least 2 weeks since prior chemotherapy

- No concurrent chemotherapy during and for at least 2 weeks after completion of study
therapy

Endocrine therapy

- Concurrent anastrozole or tamoxifen allowed

Radiotherapy

- No prior radiotherapy for the current malignancy

Surgery

- See Disease Characteristics

Other

- No prior nonhormonal therapy for the current malignancy