Trastuzumab With or Without Tamoxifen in Treating Women With Progressive Stage IV Breast Cancer

You may be eligible if

• DISEASE CHARACTERISTICS:
• Histologically confirmed invasive stage IV breast cancer
• Hormone receptor status:
• HER2/neu positive (3+ by immunohistochemical \[IHC\] assay or fluorescent in situ hybridization \[FISH\])
• Estrogen receptor or progesterone receptor positive
• Measurable or evaluable disease
• Must have disease progression within 6 months of initiation of tamoxifen (administered in the adjuvant or metastatic setting) or during aromatase inhibitor therapy
• PATIENT CHARACTERISTICS:
• Age
• 18 and over
• Sex
• Female
• Performance status
• ECOG 0-2
• Hematopoietic
• Absolute neutrophil count at least 1,000/mm\^3
• Platelet count at least 75,000/mm\^3
• Hepatic
• Bilirubin no greater than 1.5 times upper limit of normal (ULN)
• SGOT and SGPT no greater than 2.5 times ULN
• Cardiovascular
• LVEF normal by MUGA
• Other
• Not pregnant or nursing
• Fertile patients must use effective nonhormonal contraception during and for at least 2 months after study completion
• No other concurrent active malignancy except nonmelanoma skin cancer
• Patients who have completed prior therapy and are at less than 30% risk of relapse are not considered to have an active malignancy
• PRIOR CONCURRENT THERAPY:
• Biologic therapy
• No prior trastuzumab (Herceptin) in the adjuvant or metastatic setting
• Chemotherapy
• No more than 1 prior chemotherapy regimen in the metastatic setting
• No concurrent chemotherapy
• Endocrine therapy
• See Disease Characteristics
• No more than 1 prior hormonal therapy regimen for metastatic disease
• Prior aromatase inhibitor therapy administered in the first-line metastatic or adjuvant setting is allowed provided there is disease progression on tamoxifen
• No other concurrent hormonal therapy except the following:
• Steroids for adrenal failure
• Hormones for nondisease-related conditions (e.g., insulin for diabetes)
• Intermittent use of dexamethasone as an antiemetic
• Vaginal estrogen (or Estring®) for vaginal dryness
• Radiotherapy
• No concurrent palliative radiotherapy except whole brain irradiation for CNS disease
• Other
• Concurrent bisphosphonates allowed
• No concurrent cardioprotective drugs