Disclosed is the use of an antagonist molecule that inhibits hepsin activation of pro-urokinase type plasminogen activator (pro-uPA) in the manufacture of a medicament for treating cancer, wherein the antagonist molecule comprises: (i) a polypeptide comprising a Kunitz domain (KD) sequence (ii) at least a portion of human hepatocyte growth factor activator inhibitor-1, -1B, or -2 (HAT-1, HAT-1B or HAI-2) (iii) an amino acid sequence having at least about 70%, 80%, 90%, 95% or 99% sequence identity to pro-uPA and which is capable of binding hepsin and which lacks a hepsin cleavage site. Also disclosed is the molecule linked to a toxin.
