An immunoglobulin (Ig) G2 monoclonal antibody targeting the proangiogenic cytokines angiopoietin 1 (Ang1) and 2 (Ang2), with potential anti-angiogenic and antineoplastic activities. Upon administration, anti-angiopoietin monoclonal antibody AMG 780 binds to Ang1 and Ang2. This prevents the binding of the angiopoietin ligands to their receptor Tie2 (TEK), an endothelial cell-specific receptor tyrosine kinase. This prevents Tie2-mediated signaling and results in an inhibition of Tie2-expressing, tumor-stimulated endothelial cell proliferation, which prevents angiogenesis and inhibits tumor cell proliferation.