Identification of Disease States and Response to Therapy in Humans by Utilizing the Biomarker EGFR for Targeted Molecular Imaging

The epidermal growth factor receptor (EGFR) plays important roles in cell proliferation, suppression of apoptosis, increased motility, and recruitment of neovasculature. Overexpressed or mutated EGFR has been an important biomarker for cancer diagnosis and molecular target for many anticancer drugs because it frequently occurs in many common human cancers. Localizing and estimating the expression of EGFR can potentially identify patients who have tumors that overexpress EGFR and would, therefore, most likely benefit from a targeted treatment to avoid overtreatment and undertreatment. Traditional biopsy methods are invasive, and analysis of the specimens is not sufficient for real-time detection of the lesions or for monitoring the therapeutic efficacy of anticancer drugs. Molecular imaging, a technology of in vivo characterization and measurement of biological processes at the cellular and molecular level, can fulfill these goals. In this review, we summarize current molecular imaging techniques including optical imaging, magnetic resonance imaging, single photon emission computed tomography, and positron emission tomography for in vivo EGFR visualization and discuss their advantages and disadvantages. Special emphasis is placed on noninvasive imaging mutant EGFR with emerging new agents and new imaging technologies to distinguish the maximum benefit to cancer patients for molecular targeted therapy.