Overexpression or hyperactivation of ErbB cell-surface receptors drives the growth of many breast cancers. Drugs, like Herceptin, that block the receptors’ signals halt tumor progression in some patients. Not all tumors respond to this treatment: some become resistant over time. Drugs that interfere with other steps in the signaling pathway may improve the response in those patients.

Marcelo Kazanietz and colleagues, University of Pennsylvania, USA, report that protein P-Rex1 is crucial for signal transmission from ErbB receptors. They also found that P-Rex1 is overexpressed in nearly 60 % of breast cancer samples tested and patients whose tumors express P-Rex1 were more likely to develop metastasis, compared with those whose tumors did not express P-Rex1.

As P-Rex1 is only expressed in some subtypes of breast tumors, it presents an excellent target for personalized medicine.

• Identification of the Rac-GEF P-Rex1 as an Essential Mediator of ErbB Signaling in Breast Cancer
  M. Soledad Sosa, C. Lopez-Haber, C. Yang, H. Wang, M. A. Lemmon et al.,
  Mol. Cell 2010, 40(6), 877-892.
  DOI: 10.1016/j.molcel.2010.11.029