Kallikreins (KLKs) belong to the serine protease family of proteolytic enzymes. Kallikrein-8 (KLK8), also called neuropsin precursor, ovasin or serine protease 19, is a 260 amino acid secreted protein involved in hippocampal plasticity. Two isoforms exist for this protein. Isoform 1 is the primary form of KLK8 found predominantly in the pancreas. Isoform 2 contains an additional 46 amino acids after amino acid 23 and is predominantly expressed in adult brain and hippocampus. Isoform 2 is not common to the mouse homolog or other primate homologs. In humans, the T to A mutation (c.71-127T>A) leads to the splice variant seen in the human brain. Both isoforms are detected in fetal brain and placenta. In some cancer cells, KLK8 expression can suppress tumor cell invasiveness and lead to a favorable clinical outcome.