SERPINE1 and ovarian carcinoma: CTCs are currently being investigated as a tool in ovarian cancer screening with the goal of producing a diagnostic “liquid biopsy.” PAI-1 is a single-chain glycoprotein encoded by the serine protease inhibitor 1 (SERPIN E1) gene, composed of roughly 380 amino acids (aa) and having a molecular mass of approximately 50 kDa (kDa) (Declerck et al., 1992).