Novel Molecular Targets for Tumor-Specific Imaging of Epithelial Ovarian Cancer Metastases

In epithelial ovarian cancer (EOC), the strongest prognostic factor is the completeness of surgery. Intraoperative molecular imaging that targets cell-surface proteins on tumor cells may guide surgeons to detect metastases otherwise not visible to the naked eye. Previously, we identified 29% more metastatic lesions during cytoreductive surgery using OTL-38, a fluorescent tracer targeting folate receptor-a (FRa). Unfortunately, eleven out of thirteen fluorescent lymph nodes were tumor negative. The current study evaluates the suitability of five biomarkers (EGFR, VEGF-A, L1CAM, integrin avb6 and EpCAM) as alternative targets for molecular imaging of EOC metastases and included FRa as a reference. Immunohistochemistry was performed on paraffin-embedded tissue sections of primary ovarian tumors, omental, peritoneal and lymph node metastases from 84 EOC patients. Tumor-negative tissue specimens from these patients were included as controls. EGFR, VEGF-A and L1CAM were highly expressed in tumor-negative tissue, whereas avb6 showed heterogeneous expression in metastases. The expression of EpCAM was most comparable to FRa in metastatic lesions and completely absent in the lymph nodes that were false-positively illuminated with OTL-38 in our previous study. Hence, EpCAM seems to be a promising novel target for intraoperative imaging and may contribute to a more reliable detection of true metastatic EOC lesions.