To determine if coagulation factor-based probes could be used to label procoagulant cancer cells under conditions of coagulation, cancer cells were suspended in PPP pretreated with an anti-FXIa antibody and GPRP and recalcified to 8 mM Ca2+ containing vehicle or fluorescently labeled FVIIa (50–500 nM), FXa (0.5–5 μM), or FIIa (0.5–10 μM) for 30 min at room temperature. The gene discussed is GPX2; the disease is cancer.