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