Color-coded Imaging Enables Fluorescence-guided Surgery to Resect the Tumor Along with the Tumor Microenvironment in a Syngeneic Mouse Model of EL-4 Lymphoma.

BACKGROUND/AIM Fluorescence-guided surgery (FGS) of cancer is an emerging technology. We have previously shown the importance of resecting both the tumor and the tumor microenvironment (TME) for curative FGS. We also previously developed a syngeneic model using the mouse lymphoma cell line EL-4, expressing red fluorescent protein (EL-4-RFP), growing in green fluorescent protein (GFP) transgenic mice, which we have used in the present report to develop FGS of the tumor microenvironment. MATERIALS AND METHODS EL-4-RFP lymphoma cells were injected subcutaneously in C57/BL6 GFP transgenic mice. EL-4-RFP cells subsequently formed tumors by 35 days after cell transplantation. Using the portable hand-held Dino-Lite digital imaging system, subcutaneous tumors were resected by FGS. Resected tumor tissues were visualized with the Olympus FV1000 confocal microscope. RESULTS Using the Dino-Lite, subcutaneous tumors and the tumor microenvironment were clearly visualized and resected. In the resected tumor, host stromal cells, including adipocyte-like cells and blood vessels with lymphocytes, were observed by confocal microscopy in addition to cancer cells by color-coded confocal imaging. The cancer cells and stromal cells in the TME were deeply intermingled in a highly-complex pattern. CONCLUSION Color-coded FGS is an effective method to completely resect cancer cells along with the stromal cells in the TME which interact in a highly-complex pattern. Microscopically, cancer cells invade the TME and vice versa. To prevent tumor recurrence, it is necessary to resect the TME along with the tumor.