PHILADELPHIA – 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. However, not all patients’ tumors respond, with some becoming resistant over time. Different drugs that interfere with other steps in the signaling pathway may improve the response of patients, yet little is known about these molecules.

Now, Marcelo G. Kazanietz, PhD, professor of Pharmacology at the University of Pennsylvania School of Medicine and colleagues, report that a protein called P-Rex1 is crucial for signal transmission from ErbB receptors. What’s more, they found that P-Rex1 is overexpressed in nearly 60 percent 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.

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