Despite progress and continued efforts to control metastatic breast cancer, no effective treatment exists for patients with malignant cells resistant to chemotherapy, certainly not against the rare cancer initiating cells-cancer stem cellsthat are characteristically primary resistant to chemotherapy.Alloreactive donor lymphocytes were previously shown to eliminate all malignant cells and result in cure [some>25 years and many>10 years disease-free survival] of otherwise incurable patients with a large variety of hematological malignancies fully resistant to maximally tolerated does of chemoradiotherapy followed by rescue with autologous or even allogeneic stem cell transplantation.