Based on our previous clinical findings on the Imaging and Phase I study using mAb B3 radiolabeled with 111IN and 90Y we have designed a follow up study of 90Y- B3 with autologous stem cell support for patients with metastatic breast carcinoma. The primary objectives of this study are to determine the dose-limiting toxicities and the maximum tolerated dose of 90Y-B3 when administered with stem cell support because 70 % of breast carcinomas express the B3 antigen. Secondary objectives are to evaluate the anti-tumor activity and the immunogenicity of this agent when given in marrow ablative doses. The study recently opened for accrual.