Co-HP competitively inhibits the rhodocytin/CLEC-2 interaction on platelets, and hematogenous metastasis of podoplanin-expressing B16F10 to the lung in mice (which depends on tumor cell–induced platelet aggregation via CLEC-2/podoplanin interaction) is inhibited by intravenous (i.v.)administration of Co-HP33. The gene discussed is PDPN; the disease is neoplasm.