Explorative study on real-time surgical tumor margins assessment with indocyanine green in dogs: preliminary results in 13 mast cell tumors and 6 soft tissue sarcomas (November 2023 - July 2024)

Near Infrared Fluorescence with indocyanine green (ICG-NIRF) represents a new frontier for guiding tumor removal [1-3]. This study explores the feasibility and utility of ICG-NIRF in guiding canine soft tissue sarcoma (STS) and mast cell tumor (MCT) excision. Dogs with STS or MCT presented for curative intent surgery (wide excision -WE or planned marginal excision -PME) were enrolled. Radical surgery, and neo-adjuvant treatments were excluded. ICG (0.5mg/kg) was intravenously injected 24h before surgeries. NIRF-camera was used to assess fluorescence, tumor-to-background-ratio (TBR) was calculated and tissues with TBR > 1.1 were considered fluorescent. Fluorescence guidance was considered changing the expected surgery if led to extend the lateral margins or to excise additional tissue from the tumor bed. NIRF guidance and the status of histological margins were recorded. Eighteen dogs with 13 MCTs and 6 STSs were enrolled. Fluorescence was present in 6/6 STSs and 11/13 MCTs (2 subcutaneous MCTs were excluded from the analysis due to NIRF failure). Overall surgical excision comprised 8 PME and 9 WE. In 11 tumors, surgical planning changed based on NIRF guidance: in 6 tumors not-infiltrated margins were obtained (5 WE and 1 PME), while 5 tumors (PME) had infiltrated margins despite the extended excision. In 3 tumors, the anatomical location did not allow additional tissue removal although indicated by NIRF, and 2 of these margins were infiltrated. In 3 tumors fluorescence did not change the surgical planning (2 WE and 1 PME): 2 had infiltrated margins. These preliminary results show the feasibility of ICG-NIRF in STS and MCT surgical visualization. Even if infiltrated margins were recorded, ICG-NIRF can be a real-time guidance during canine tumor excision and might help minimize the risk of infiltrated margins. Larger population studies are needed to confirm this hypothesis and to plan the next milestones in clinical research.