Tumor-associated trypsin inhibitor (TATI) is a low-molecular-weight (6 kDa) trypsin inhibitor that has been used as a marker for ovarian cancer. It is also expressed together with tumor-associated trypsin by many other tumors, and increased serum concentrations of TATI occur in connection with these. TATI is a prognostic marker for ovarian, bladder, and kidney cancer, which may be associated with the participation of trypsin in protease cascades contributing to tumor invasiveness.