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Met Receptor Contributes to Trastuzumab Resistance of Her2-Overexpressing Breast Cancer Cells

University of California Davis Cancer Center, Sacramento, California

Requests for reprints: Colleen Sweeney, University of California Davis Cancer Center, Research Building III, Room 1400C, 4645 2nd Avenue, Sacramento, CA 95817. Phone: 916-734-0726; Fax: 916-734-0190; E-mail: casweeney{at}ucdavis.edu.

Key Words: Trastuzumab resistance • Her2 • Met receptor

Her2 is overexpressed in 20% to 30% of breast tumors and correlates with reduced disease-free and overall patient survival. Trastuzumab, a humanized monoclonal antibody directed against Her2, represents the first Her2-targeted therapy, which decreases the risk of relapse and prolongs patient survival. Resistance to trastuzumab, both inherent and treatment-acquired, represents a significant barrier to the effective treatment of Her2 (+) breast cancer. The Met receptor tyrosine kinase is aberrantly expressed in breast cancer and predicts poor patient prognosis. In this study, we find that Met is frequently expressed in Her2-overexpressing breast cancer cells, as well as Her2 (+) breast cancer. Importantly, Met contributes to trastuzumab resistance, as inhibition of Met sensitizes cells to trastuzumab-mediated growth inhibition, whereas Met activation protects cells against trastuzumab by abrogating p27 induction. Remarkably, Her2-overexpressing breast cancer cells rapidly up-regulate Met expression after trastuzumab treatment, promoting their own resistance. Our study suggests that a subset of Her2 (+) patients may benefit from combined inhibition of Her2 and Met. [Cancer Res 2008;68(5):1471–7]

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