To differentiate between matriptase and uPA proteolytic activities in these xenograft tumor models we have used Probody probes directed against EGFR and containing a substrate cleavable by both matriptase and uPA (Pb-S01), or Probody construct Pb-S02 (Probody-S02) containing a uPA selective substrate (TGRGPSWV)18. The gene discussed is EGFR; the disease is neoplasm.