Feasibility of folate receptor-targeted intraoperative fluorescence imaging during staging procedures for early ovarian cancer

Objectives: Completeness of staging is an independent prognostic factor for survival in surgical staging procedures for early ovarian cancer. Near-infrared (NIR) fluorescence imaging has the potential to improve the intraoperative assessment of metastatic spread and thus completeness of staging. Feasibility of folate receptor alpha (FRα) targeted fluorescence imaging using OTL-38, a folate analogue conjugated to an NIR fluorescent dye, has been previously demonstrated in advanced ovarian cancer. The present authors hypothesized that in early ovarian cancer, fluorescence imaging using OTL-38 could lead to more accurate detection of (occult) ovarian cancer metastases, allowing gynecologic surgeons to take targeted rather than blind biopsy samples. Materials and Methods: Six patients scheduled to undergo a staging procedure for suspected early stage ovarian cancer, received an intravenous infusion of 0.0125 mg/kg OTL38 2-3 hours prior to surgery. The authors assessed tolerability, pharmacokinetics, and the feasibility of intraoperative NIR fluorescence detection of ovarian cancer lesions. Feasibility was evaluated using histopathological analysis, tumor-to-background ratio, and number of false positive and negative lesions. Results: Distinction between a malignant and benign primary tumor was possible with OTL-38 based fluorescence imaging. In addition, nine fluorescent lesions, all lymph node (LN) clusters, were detected intraoperatively. Tumor cells were not demonstrated in any of the biopsy samples taken during staging procedures, including the fluorescent lesions. Therefore all fluorescent LNs were false positives. Conclusions: Metastatic lesions were not present in the patients with confirmed early ovarian cancer; hence the anticipated added value of NIR fluorescence imaging could not be demonstrated in this study. Fluorescence imaging led to resection of non-malignant LNs, as comprehensive lymph node dissection should be pursued in surgical staging procedures, this should not impede application of OTL38. Importantly, fluorescence imaging allowed distinction between a malignant and benign primary tumor and had no false negatives.