Osteosarcoma (OS) is the most common primary bone cancer in children and, unfortunately, is associated with poor survival rates. OS most commonly arises around the knee joint, and was traditionally treated with amputation until surgeons began to favour limb-preserving surgery in the 1990s. Whilst improving functional outcomes, this was not without problems, such as implant failure and limb length discrepancies. OS can also arise in areas such as the pelvis, spine, head, and neck, which creates additional technical difficulty given the anatomical complexity of the areas. We reviewed the literature and summarised the recent advances in OS surgery. Improvements have been made in many areas; developments in pre-operative imaging technology have allowed improved planning, whilst the ongoing development of intraoperative imaging techniques, such as fluorescent dyes, offer the possibility of improved surgical margins. Technological developments, such as computer navigation, patient specific instruments, and improved implant design similarly provide the opportunity to improve patient outcomes. Going forward, there are a number of promising avenues currently being pursued, such as targeted fluorescent dyes, robotics, and augmented reality, which bring the prospect of improving these outcomes further.

Background: Sarcomas are rare, aggressive cancers which can occur in any region of the body. Surgery is usually the cornerstone of curative treatment, with negative surgical margins associated with decreased local recurrence and improved overall survival. Indocyanine green (ICG) is a fluorescent dye which accumulates in sarcoma tissue and can be imaged intraoperatively using handheld near-infrared (NIR) cameras, theoretically helping guide the surgeon’s resection margins. Methods: Patients operated on between 20 February 2019 and 20 October 2021 for intermediate to high grade sarcomas at our centres received either conventional surgery, or were administered ICG pre-operatively followed by intra-operative NIR fluorescence guidance during the procedure. Differences between the unexpected positive margin rates were compared. Results: 115 suitable patients were identified, of which 39 received ICG + NIR fluorescence guided surgery, and 76 received conventional surgery. Of the patients given ICG, 37/39 tumours fluoresced, and surgeons felt the procedure was guided by the intra-operative images in 11 cases. Patients receiving ICG had a lower unexpected positive margin rate (5.1% vs. 25.0%, p = 0.01). Conclusions: The use of NIR fluorescence cameras in combination with ICG may reduce the unexpected positive margin rate for high grade sarcomas. A prospective, multi-centre randomised control trial is now needed to validate these results.

Introduction: Indocyanine green (ICG) is a near infrared (NIR) dye which has been used clinically for over 50 years and has recently been utilised for fluorescence guided surgery in a number of cancer types, including sarcoma. ICG is taken up and retained by sarcoma tumours to a greater extent than normal tissue, demonstrating its potential to aid in visualisation of tumour margins. However, the mechanisms surrounding preferential ICG uptake in tumours are poorly understood. Methods: In vitro ICG cellular uptake studies were performed across a panel of four sarcoma cell lines and one breast cancer cell line, exhibiting varying proliferation rates and phenotypes. The effects of ICG concentration, incubation time, inhibition of clathrin mediated endocytosis and cell line proliferation rate on the cellular uptake of ICG were investigated using fluorescence microscopy and flow cytometry. The spatial orientation of ICG was also assessed in a patient specimen. Results: The level of ICG cellular uptake was dependent on ICG concentration and incubation time. Cell line proliferation rate correlated significantly to ICG uptake within 30 minutes (Rs= 1, p<0.001), whilst retention of ICG after 24hrs did not (Rs= 0.3, p=0.624). From our data, the primary mechanism of ICG uptake in sarcoma cells is via clathrin mediated endocytosis. Following the resection of a grade 3 leiomyosarcoma, ICG signal was detectable macroscopically and on 3μm sections, whilst being negative on the muscle control. Conclusions: The use of ICG for tumour detection in sarcoma surgery may demonstrate higher utility in high grade tumours compared to low grade tumours, due to the observation of higher ICG uptake in more proliferative cell lines. It is likely that the enhanced permeability and retention (EPR) effect plays a significant role in the retention of ICG within tumours. Future work on the detection of ICG at the cellular level within human tissue sections is required, with the aid of purpose built NIR microscopes.

Indocyanine green (ICG) is a well‐established near‐infrared dye which has been used clinically for several decades. Recently, it has been utilised for fluorescence‐guided surgery in a range of solid cancer types, including sarcoma, with the aim of reducing the positive margin rate. The increased uptake and retention of ICG within tumours, compared with normal tissue, gives surgeons a visual reference to aid resection when viewed through a near‐infrared camera. However, the mechanisms of this process are poorly understood. We performed in vitro ICG cellular uptake studies across a panel of sarcoma cell lines exhibiting varying proliferation rates and phenotypes. The effects of ICG concentration, incubation time, inhibition of clathrin‐mediated endocytosis, and cell line proliferation rate on the cellular uptake of ICG were investigated using fluorescence microscopy and flow cytometry. Subcellular localisation of intracellular ICG was assessed via colocalization with a lysosomal marker. The spatial distribution of ICG in patient tumour tissue following fluorescence‐guided surgery was assessed by high‐resolution tissue imaging and quantified using fluorescence lifetime imaging. In vitro results showed that the cell line proliferation rate correlated significantly with ICG uptake (Spearman's rank correlation coefficient = 1.00, p < 0.001), and maximum ICG uptake was observed after 24 h incubation. ICG cellular uptake was significantly reduced by inhibition of clathrin‐mediated endocytosis (p = 0.0004), and intracellular ICG significantly colocalized with a lysosomal marker within 30 min (Pearson's r = 0.8). On histological analysis of tumour tissue from three different sarcoma subtypes, ICG was observed within sarcoma cells as well as accumulating in paucicellular areas of haemorrhage and necrosis within the tumour microenvironment. Through quantification of fluorescence lifetime imaging of ICG, we were able to differentiate sarcoma cells from haemorrhage and necrosis within tumour tissue. Combining in vitro data with analysis of patient tissue, we propose that the uptake and accumulation of ICG in sarcomas is driven by a synergistic mechanism involving the enhanced permeability and retention effect combined with active tumour cell endocytosis of the dye. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.