This application proposes to extend results from a Phase I study which examined mechanisms to enhance the investigators' Micrometastases Clonogenic Assay (MCA) for the in vitro growth of tumor colonies from bone marrow specimens of breast cancer patients. Phase II studies will test the ability of the MCA assay to predict drug sensitivity/resistance in the high-dose chemotherapy/autologous bone marrow transplantation setting. The goal is to assist transplant physicians to identify those patients most likely to benefit from further treatment, such as high-dose chemotherapy, by determining the drug sensitivity/resistance of established metastatic disease prior to treatment.