Real-time tumor fluorescence guided surgery with indocyanine green: an explorative study in canine soft tissue sarcomas and mast cell tumors

Near Infrared Fluorescence (NIRF) with indocyanine green (ICG) represents a new frontier with promising results for guiding tumor removal, but, to date, limited information is available in dogs. [1-3] Due to their various anatomical locations, canine soft tissue sarcomas (STS) and mast cell tumors (MCT) often may imply challenging surgical dose management. This study wants to explore the feasibility and utility of the real-time tumor fluorescence guided surgery (TFGS) with NIRF-ICG in canine STS and MCT excision. Owned-dogs with spontaneous STS or MCT at first presentation or recurrence, eligible for curative intent surgery were enrolled for TFGS with NIRF-ICG. A dose of 0.5 mg/kg of ICG was intravenously injected 24 hours before the surgery. Before the TFGS, the surgeon drew the planned skin margins. Then a NIRF-camera (SPY-PHI QP system-Stryker) was used to real-time quantify the fluorescence intensity of the tumor and the surrounding tissues (background) and the tumor-to- background-ratio (TBR) was intraoperatively calculated. The TFGS was considered feasible if the tumor fluorescence was distinguishable from the surrounding tissues and TBR ≥ 2. The NIRF-ICG was employed to real-time direct the surgeon in all the tumor excisional phases. After the tumor removal, the surgeon used NIRF to assess the wound bed and, if present and if possible, residual fluorescent tissues were removed. The TFGS data collected were: feasibility, extension of the planned surgical dose, the presence of residual fluorescence in wound bed and its relation with the histopathological status of margins. Twenty-four dogs with 26 tumors (14 MCTs and 12 STSs) were included. The TFGS was feasible in 12/12 STS (100%) and in 11/14 MCT (79%), since 3 subcutaneous MCTs with TBR <2 were excluded from the analysis. The median TBR registered in STS and MCT was respectively 11,9 and 5,8. The TFGS led to the extension of the surgical dose in 8/12 STS (67%) and in 6/11 MCT (55%). Among them 4/8 STS (50%) and 2/6 MCT (33%) had infiltrated margins despite the increase of the surgical dose. Residual fluorescence was identified in the wound bed after the excision of 4/12 STS (33%) and in 5/11 MCT (45%). In 2/4 STS (50%) and 3/5 MCT (60%) the presence of residual fluorescence in the wound bed was related to infiltrated histological margins (real positive) and the sensitivity and specificity of the TFGS were respectively 50% and 75% for STS, and 60% and 50% for MCT. These preliminary results convey the feasibility of TFGS with NIRF-ICG in both canine STS and MCT surgical extirpation. NIRF-ICG guidance may help to minimize the risk of infiltrated margins or, at least, to reduce the tumor burden. According to this study results, NIRF-ICG is promising in tumor guided removal for STS, while the failures and the lower TBR observed in MCT, may imply that NIRF-ICG is less efficient for this histotype. The different performance in the histotypes should be investigated in a larger population including follow-up data and time of local recurrence.