A humanized IgG1 monoclonal antibody directed against the placenta growth factor (PGF), with potential anti-angiogenic and antineoplastic activities. Anti-PGF monoclonal antibody RO5323441 binds to both PGF-1 and -2, thereby inhibiting the binding of PGF-1 and -2 to the vascular endothelial growth factor receptor-1 (VEGFR-1) and subsequent VEGFR-1 phosphorylation. This may result in the inhibition of tumor angiogenesis and tumor cell proliferation. PGF, a member of the VEGF sub-family and a key molecule in angiogenesis and vasculogenesis, is upregulated in many cancers.