Trypsin activity is properly suppressed by pancreatic secretory trypsin inhibitor (PSTI), which is also known as serine protease inhibitor Kazal type 1 (SPINK1), thereby preventing damage to pancreatic acinar cells as the first line of defense. SPINK1 is a 6420 Da peptide produced by the pancreas, but also by several other tissues and many tumors. SPINK1, which is an acute-phase response protein plays a role in protecting the pancreas against premature activation of trypsinogen and is involved in cancer progression. SPINK1 promoted LAC cell growth, migration, and invasion. Some mutations of the SPINK1 gene, like the one causing amino acid change N34S, have been shown to confer susceptibility to recurrent or chronic pancreatitis. Detection of such variants is therefore of clinical utility. SPINK1 overexpression defines the second most recurrent and aggressive prostate cancer subtype.