Protein tyrosine phosphatases and breast cancer.

Protein tyrosine phosphatases (PTPs) consist of a large family of related enzymes, including the group of classical PTPs with its two main subgroups, the transmembrane receptor-type (RPTPs) and the intracellular or non-transmembrane PTPs. Published data on the expression and function of a panel of these enzymes in normal and cancerous breast tissues are discussed in this review. While most studies, albeit on different enzymes, have tended to agree on the evidence for an increased PTP expression in breast cancer, any connection between PTP expression and the enzymes' role in cancer development and progression remains largely open to interpretation. Concomitant increases of protein tyrosine kinase (PTK) and PTP activities in many cancers further indicate that a complex dysregulation in the balance of tyrosine phosphorylation could be responsible for major alterations in various cellular processes controlling tissue homeostasis. In particular, any relationship between the expression of PTPs and their specific diverse roles in the regulation of cell growth and apoptosis in breast cancer needs to be addressed in major fundamental, preclinical and clinical studies.