Protein tyrosine phosphatase-PEST (PTPN12), a ubiquitously expressed cytoplasmic tyrosine phosphatase, is thought to play an important role in cell adhesion and motility, cell migration, and signal transduction for antigen receptors in B and T lymphocytes. Signal transduction via tyrosine phosphorylation, normally fine-tuned by the concerted action of both protein tyrosine kinases and protein tyrosine phosphatases (PTPs), is a key mechanism in tumorigenesis. Studies suggest potential role for PTP-PEST in regulation of p130(cas) in mitogen- and cell adhesion-induced signaling events.