SUN-746 Effective Treatment of Tumour Induced Osteomalacia With Combined Percutaneous Radiofrequency Ablation and Surgical Bone Cement

Abstract Disclosure: T.J. Block: None. M. Pritchard: None. M.J. Thompson: None. Background: Tumour-induced osteomalacia (TIO) is a paraneoplastic syndrome caused by phosphaturic mesenchymal tumours (PMTs) that secrete fibroblast growth factor 23 (FGF23). Tumour resection is often challenging due to tumour location. Radiofrequency ablation (RFA) has demonstrated effectiveness in small series and case reports, although long-term efficacy is unknown. Presentation: A 62-year-old female presented with a 5-year history of profound skeletal fragility with numerous fractures despite potent antiresorptive and osteoanabolic treatment. She first presented at age 58 with 12 months of lumbar, hip, and bilateral foot pain associated with prominent myalgias. Imaging demonstrated severe osteoporosis and minimal trauma vertebral, rib, pelvic and metatarsal fractures. A secondary osteoporosis screen was negative. She was treated with teriparatide followed by denosumab with an improvement in bone mineral density (BMD). However, she continued to experience numerous atraumatic fractures and pronounced myalgias resulting in progressive disability. She became dependent on walking aids to ambulate, resigned from work and was unable to pursue her favourite pastime, golf, or play with her grandchildren. Repeat biochemical evaluation revealed an acquired and persistent severe hypophosphatemia, renal phosphate wasting and elevated serum FGF23. 68Ga-DOTA PET/CT demonstrated an avid focus in the right acetabulum, corresponding to a 13 mm well-circumscribed lucent lesion on CT. A diagnosis of TIO due to an acetabular PMT was made and preoperative treatment with oral phosphate and calcitriol commenced. This resulted in normalisation of serum phosphate and rapid improvement in myalgias and bone pain. She became able to ambulate independently. Surgical resection would have required hemi-pelvectomy and therefore percutaneous AIRO® CT-guided RFA with injection of Surgical Simplex™ P bone cement was performed. Serum phosphate and FGF23 subsequently normalised and renal phosphate wasting resolved when evaluated 4 weeks after ceasing phosphate and calcitriol. She experienced a sustained improvement in symptoms and wellbeing and was able to resume golf and playing with her grandchildren. At 18 months post procedure she remains in clinical, biochemical, and radiological remission without further fractures and with significant improvements in BMD consistent with remineralisation. Discussion: There is a well described delay between initial symptoms and final diagnosis for patients with TIO. This can result in significant morbidity and emphasises the importance of serum phosphate assessment in the evaluation of skeletal fragility. Imaging-guided RFA can be effective when surgical intervention is not appropriate. Polymerisation temperatures of polymethylmethacrylate bone cement can exceed 80°C causing thermal necrosis. This may provide additional local disease control. Presentation: Sunday, July 13, 2025