A humanized monoclonal antibody directed against the platelet-derived growth factor receptor (PDGFR) alpha with potential antineoplastic activity. Anti-PDGFR alpha monoclonal antibody MEDI-575 inhibits activation of the cell-surface tyrosine kinase PDGFR alpha subunit and subsequent triggering of mitogenic signaling pathways, including the JAK/STAT, PI3K/Akt, and MAP kinase pathways. PDGFR alpha acts as a mitogenic signaling receptor for cells of mesenchymal origin and inhibition of receptor activity may inhibit tumor cell proliferation.