Nephrogreen. Appearances of Exvivo Renal Tumours Under Near-infrared

Overview

Indocyanine Green (ICG) is a dye which fluoresces under near-infrared (NIR) light. It has been used for several applications in adult surgery. The CI is pioneering its use in children's kidney cancer surgery for lymph node identification and removal. This study concentrates on its use for procedures where only the part of the kidney containing tumour is removed. It is known that kidney tumours in both adults and children do not take up ICG at all. This absence of uptake can be used to define the border between normal and abnormal renal tissue giving a real-time picture of the area of tumour. This then delivers surgeons an intra-operative roadmap for removing only the cancerous part of the kidney. At present the international society of paediatric oncology - renal tumour study group (SIOP-RTSG) protocol, which is followed in the UK, advises consideration of partial nephrectomy for children with bilateral renal tumours and in children with unilateral tumours who have a renal tumour predisposition syndrome. There is ongoing debate about partial nephrectomy in unilateral renal tumour surgery in children who do not have a predisposition syndrome. This study aims to provide the evidence that paediatric renal tumours do not take up ICG at a naked-eye level and confirm this at a cell level. ICG will be infused into kidneys containing tumour once they have been removed from the patient, The kidney and tumour will be observed under NIR light to show where the areas of fluorescence are. Then, a pathologist will prepare the specimen in theatre, in the same way they would do in the lab. The specimen would be bivalved and reviewed under NIR. Microscopy specimens of the border between normal and abnormal tissue would then be reviewed with an NIR capable microscope. The standard histopathological assessment would then take place.

This study will ascertain if paediatric renal tumours are ICG avid or not. This is critical for determining what the value of using ICG/NIRF will be during nephron sparing surgery (NSS)/ partial nephrectomy in children who have renal tumours that are suitable for this type of surgery. If the normal renal parenchyma is ICG avid but the tumour is not (as has been shown for RCC in adults) then we can conclude that if a fluorescent margin left in-situ on the tumour, then it would be completely resected. Early work at St. Jude has suggested this technique shows promise, but it has not been validated prospectively at a macro or microscopic level. This is important because in children with unilateral tumours, total nephrectomy has been performed routinely due to concern over leaving behind tumour tissue. If tumour tissue is left behind the patient is upstaged and requires radiotherapy with the consequent sequelae that confers. Radiotherapy to this area invariably damages the kidney so much that it is essentially non-functioning and avoiding this exposure would clearly be ideal. In children with bilateral tumours, retaining as much renal tissue as possible whilst facilitating a complete resection is the goal of surgery. If ICG/NIRF can help with this then it will change the game for this population of patients In addition, this technique will aid in retaining as much normal parenchyma as possible giving the patient better long-term outcomes for renal function. As a further advantage, the study may ascertain if ICG can differentiate between non-cancerous nephrogenic rests (NRs), normal renal parenchyma, and tumour. The difference between these types of tissue is critical when doing NSS because currently only formal histopathological assessment can reliably differentiate NRs from normal tissue or tumour. This is because the definition hinges on whether the lesions have a capsule or not. This is not identifiable on imaging or on core biopsy. The vital feature is that NR's do not require resection, whereas tumour obviously does. Avidity for ICG may be different in different types of tumours and this will be recorded using the intensity mapping feature of the Storz Rubina Opal1 system. At a cellular level it will be important to investigate why ICG does not cross into tumour and whether this is due to the tumour capsule preventing or limiting vascular flow, or some other factor. ICG does not affect the histopathological assessment and this research study will validate whether ICG survives the fixing process as this has not been assessed with an NIR capable microscope.