We have identified a new tumor growth factor for multiple myeloma (MM) called pleiotrophin (PTN). PTN levels are higher in the blood of MM patients. An anti-PTN antibody slowed tumor growth and blood vessel development in MM laboratory models. These results suggest that a therapeutic antibody could provide an important new anti-MM treatment. We propose to develop this new PTN-antibody and test its effects on MM in preclinical studies. We will also determine the proteins that PTN targets on the surface of myeloma cells. These studies will provide support for the clinical development of a new therapy for myeloma patients.