PSP94BP (PSPBP, Peptidase inhibitor 16, CRISP-9, PI-16) is a cell-surface-expressed type II transmembrane serine protease and was identified as one of the most highly upregulated genes in prostate cancer. PSP94BP protein expression was highest at sites of bone metastasis and in late-stage primary tumor, suggesting a role in tumor progression. In accordance, in vivo studies demonstrated that overexpression of PSP94BP led to tumor progression and metastasis. As PSP94BP expression correlates well with prostate cancer progression, it was proposed as a diagnostic marker and target for prostate cancer therapy.