Trastuzumab for 6 Months or 1 Year in Treating Women With Nonmetastatic Breast Cancer That Can Be Removed By Surgery

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. It is not yet known whether giving trastuzumab for 6 months is as effective as giving trastuzumab for 1 year in treating patients with breast cancer. PURPOSE: This randomized phase III trial is studying trastuzumab to see how well it works when given for 6 months compared to 12 months in treating women with nonmetastatic breast cancer that can be removed by surgery.