In this study, we present a novel approach for the induction of tumor vessel thrombosis using genetically modified coagulation factor X. Human factor X was engineered in its activation peptide in a way that it can be specifically activated by prostate-specific antigen (PSA), a tumor-specific proteinase secreted into the bloodstream by prostate cancer cells. For this purpose we inserted different sequences of known PSA cleavage sites from the natural substrate of PSA, semenogelin I, into the activation peptide of factor X. One FX variant (FX-V4) was further optimized by site-directed mutagenesis of the P2 position and the P5 position (FX-V4-P2YP5R). After preincubation with PSA, FX-V4-P2YP5R was able to efficiently induce coagulation in vitro. These FX variants should be useful for site-specific induction of blood coagulation in the tumor vasculature.