Use of Porphysomes to detect primary tumour, lymph node metastases, intra-abdominal metastases and as a tool for image-guided lymphadenectomy: proof of concept in endometrial cancer

Objective: To investigate Porphysome fluorescence image-guided resection (PYRO-FGR) for detection of uterine tumour, metastatic lymph nodes and abdominal metastases in a model of endometrial cancer. Methods: White New Zealand rabbits were inoculated with VX2 cells via intra-myometrial injection. At 30 days, Porphysomes were administered intravenously. At 24 h the abdomen was imaged and fluorescent tissue identified (PYRO-FGR). After complete resection of fluorescent tissue, fluorescence-negative lymph nodes and peritoneal biopsies were removed. Histopathology including ultra-staging and analysis by a pathologist was used to detect tumour. Fluorescence signal to background ratio (SBR) was calculated and VX2 (+) tissue compared to VX2 (-) tissue. Biodistribution was calculated and Porphysome accumulation in fluorescent VX2 (+) tissue compared to fluorescent VX2 (-) and non-fluorescent VX2 (-) tissue. Results: Of 17 VX2 models, 10 received 4 mg/kg of Porphysomes and 7 received 1 mg/kg. Seventeen tumours (UT), 81 lymph nodes (LN) and 54 abdominal metastases (AM) were fluorescence-positive and resected. Of these, 17 UT, 60 LN and 45 AM were VX2 (+), while 16 LN and 5 AM were VX2 (-). Nine specimens were excluded from analysis. Thirty-one LN and 53 peritoneal biopsies were fluorescence-negative and resected. Of these, all LN and 51/53 biopsies were VX2 (-) with only 2 false-negative biopsies. Sensitivity and specificity of PYRO-FGR for VX2 (+) tissue was 98.4% / 80.0% overall, 100% / 100% for UT, 100% / 66.0 % for LN and 95.7% / 91.4% for AM. Increased SBR and biodistribution was observed in VX2 (+) tissue vs. VX2 (-) tissue. Conclusions: Porphysomes are a highly sensitive imaging agent for intra-operative detection and resection of uterine tumour, metastatic lymph nodes and abdominal metastases.