Real-world outcomes in patients with tumor-induced osteomalacia treated vs not treated with burosumab

Context: Tumor-induced osteomalacia (TIO) is an ultra-rare condition caused by tumors secreting fibroblast growth factor-23, leading to chronic hypophosphatemia, pain, muscle weakness, fractures, and impaired physical function. Burosumab is a monoclonal antibody indicated for treatment of TIO when tumors cannot be curatively resected. Objective: This study compares clinical and patient-reported outcomes in patients with TIO treated vs not treated with burosumab in a real-world setting. Design: This interim analysis reports outcomes at enrollment in the prospective, observational Tumor-Induced Osteomalacia Disease Monitoring Program (NCT04783428), stratified by burosumab treatment status at enrollment. Setting: Tertiary care centers in the United States and Argentina. Patients: Patients with TIO from the Disease Monitoring Program. Exposure: Burosumab treatment. Main outcome measures: Biochemistry measurements and patient-reported health-related quality of life (pain, fatigue, and physical function). Results: 21 patients with TIO (61.9% female, median [Q1, Q3] age 49.7 years [41.6, 57.3]) were included. At enrollment, 11 (52.4%) patients were treated with burosumab, for a median (Q1, Q3) duration of 4.1 years (0.8, 7.0). Burosumab-treated patients had significantly higher serum phosphate and 1,25-dihydroxyvitamin D levels, and nonsignificantly lower alkaline phosphatase levels, compared with patients not treated with burosumab. Patients treated with burosumab reported significantly lower median Brief Pain Inventory scores, nonsignificantly lower Brief Fatigue Inventory scores, and nonsignificantly higher Patient-Reported Outcomes Measurement Information System Physical Function and Short-Form-36 scores, indicating lower symptom severity and better health-related quality of life. Conclusion: This study suggests favorable biochemical and patient-reported outcomes in patients with TIO treated with burosumab.