Near-infrared Intraoperative Molecular Imaging Can Identify Metastatic Lymph Nodes in Prostate Cancer

Objective To propose a novel method to perform indocyanine green (ICG) based near-infrared (NIR) fluorescence imaging during pelvic lymph node dissection (PLND) for prostate cancer patients with lymph node metastasis (LNM). Materials and Methods A prostate cancer cell line PC3 was used to establish xenograft model in NOD/SCID mice. After tumor growth, the mice were injected with ICG through the tail vein. Xenografts and surrounding tissues were imaged with NIR camera 24 hours after intravenous ICG, and tumor-to-background ratios were calculated. We then performed a pilot human study to evaluate the role of NIR imaging in robotic PLND after systemic ICG in 4 patients with prostate cancer and preoperative lymphadenopathy. Results ICG localized to PC3 xenografts in the mice and all xenografts were highly fluorescent compared with surrounding tissues, with a median tumor-to-background ratio of 2.85 (interquartile range = 2.64-3.90). In the human study, intraoperative in vivo NIR imaging identified 3 of the 4 preoperative lymphadenopathies as fluorescence-positive, and back table ex vivo NIR imaging identified all 4 lymphadenopathies as fluorescence-positive. All the lymphadenopathies were found to be LNMs by pathologic examination. Two of the four cases had additional LNMs, all of which were fluorescence-positive with intraoperative in vivo NIR imaging. Conclusion Intravenously administered ICG accumulates in prostate cancers in both a murine model and human patients. NIR fluorescence based on intravenous ICG may serve as a useful tool to facilitate the identification of positive nodes during PLND in patients with higher risk of LNMs.