PSOC

RATIONALE: Monoclonal antibodies, such as trastuzumab, can block tumor growth in different ways. Some block the ability of tumor cells to grow and spread. Others find tumor cells and help kill them or carry tumor-killing substances to them. Radiation therapy uses high-energy x-rays to kill tumor cells. It is not yet known whether radiation therapy is more effective with or without trastuzumab in treating ductal carcinoma in situ.

PURPOSE: This randomized phase III trial is studying radiation therapy to see how well it works compared with or without trastuzumab in treating women with ductal carcinoma in situ who have undergone lumpectomy.

DISEASE CHARACTERISTICS:

• Histologically confirmed ductal carcinoma in situ (DCIS)

  • Mixed DCIS and lobular carcinoma in situ (LCIS) allowed
• HER2 receptor-positive as determined by central testing

• Must have undergone resection by lumpectomy and meets the following criteria:

  • Margins of the resected specimen must be histologically free of DCIS (re-excision to obtain clear margins allowed)
  • No more than 120 days since the last surgery for excision of DCIS (lumpectomy or re-excision of lumpectomy margins)

• None of the following allowed:

  • Patients who require mastectomy
  • Invasive (including microinvasion staged as T1mic) breast cancer (DCIS "suspicious" for microinvasion, but not confirmed, allowed)
  • Nodal staging of pN1 (including pN1mi) (axillary staging not required)
  • DCIS present in more than one quadrant (multicentric)
  • Masses or clusters of calcification that are clinically or mammographically suspicious unless biopsied and proven to be benign
  • Contralateral breast cancer (including DCIS)
  • History of breast cancer, including DCIS (history of LCIS allowed)

• Hormone receptor status:

  • Estrogen receptor and/or progesterone receptor-positive or -negative
• Must submit tumor block for correlative studies