Intraoperative molecular imaging can identify sub-centimeter peritoneal implants during ovarian cancer cytoreductive surgery

Objective: To investigate the impact of fluorescent imaging on intraoperative identification of sub-centimeter tumor implants as a means of improving detection and removal of cancer deposits. Materials and Methods: In order to confirm the distribution of the folate receptor alpha (FRα), sections of 20 ovarian tumors and seven normal ovarian tissues were obtained and immunohistochemistry was performed using monoclonal antibody mAb343 to evaluate FRα expression. To investigate the value of fluorescent imaging in vivo in ovarian cancer surgery, an animal xenograft model was used. NOD/SCID/Gama mice were subcutaneously or intra-peritoneally injected with IGROV-1, SKOV3, KB cells, and IOSE cells. Surgical evaluation of the tumor infiltrated area was done after the folateFITC conjugate infusion. The surgeon’s visual inspection and palpitation was used first and thereafter fluorescence imaging was applied to determine if additional nodules could be located. In addition, for further in vivo evaluation, five human patients with ovarian cancer were systemically infused with 0.1 mg/kg of the folate-FITC conjugate four hours prior to cytoreductive surgery. During the standard of care operation, the surgeons performed the standard approach and inspected the body cavity for tumor nodules using unaided visual inspection and palpation followed by examination with fluorescence imaging. The authors analyzed the tumor background ratio (TBR) to tumor size for each nodule. Results: Seventeen out of 20 tumors displayed moderate (2+) to strong (3+) expression of FRα with no staining of surrounding stroma. Using fluorescence microscopy, fluorescent dye uptake was seen uniformly on IGROV-1 and SKOV3 cell lines and the intensity peaked at one hour and localized to the cell surface with cytosolic staining. By Day 14, the surgeon, without intraoperative imaging, identified an average of seven nodules per animal (range 0-12), whereas the surgeon could identify a mean of 11 nodules (range 0-18, p < 0.03) with intraoperative imaging. In triplicate experiments, the addition of the intraoperative imaging allowed investigators to locate one to five more nodules per mouse (mean 3.8, p < 0.01). The peak TBR in the primary tumor to normal tissue was at four hours. At that time point, the TBR was 23.6 ± 8.7. In human evaluation, no toxicity was detected. Conclusions: Intraoperative fluorescent imaging of FRα positive ovarian cancer increased the removal of residual disease in murine model effectively during debulking surgery. The application of the technology in human requires future human studies.

Ovarian carcinoma; Folate receptor; Fluorescence imaging; Cytoreduction; Molecular imaging.

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