In conclusion, we are starting to uncover important activities of PTPs in breast cancer initiation, progression and maintenance. Studies of SHP2 and PTP1B have exposed them as potentially important targets for the treatment or prevention of breast cancer, not to mention the importance of PTP1B in diabetes. However, the appropriateness of specific inhibitors has to be fully confirmed, especially given the differential involvement of PTPs in an organ-dependent fashion. Crucial issues for future studies include the participation of other PTPs in tissue development and maintenance as well as cancer, and the signaling networks perturbed by PTP inactivation. This approach may lead to the discovery of novel signaling mechanisms regulated by PTPs and a better understanding of cancer-associated pathways.