Figure 9: Subcutaneously implanted tumors expressing HER1 (arrowheads) or expressing HER2 receptors (arrows). Two optically labeled antibodies, Cy5.5-cetuximab (anti-HER1; red) and Cy7-trastuzumab (anti-HER2; green), were injected and imaging was performed. The tumors cannot be differentiated on (a) the white light image, but with (b) fluorescence imaging, the two different tumor types are clearly distinguished.