Docetaxel and Trastuzumab With or Without Carboplatin in Treating Women With HER2-Positive Breast Cancer

RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Monoclonal antibodies such as trastuzumab can locate tumor cells and either kill them or deliver tumor-killing substances to them without harming normal cells. It is not yet known if docetaxel and trastuzumab are more effective with or without carboplatin in treating women who have HER2-positive breast cancer. PURPOSE: Randomized phase III trial to study the effectiveness of combining docetaxel and trastuzumab with or without carboplatin in treating women who have HER2-positive stage IIIB or stage IV breast cancer.