Background/Purpose: Tumor-induced osteomalacia (TIO) is an ultra-rare paraneoplastic disorder, characterized by renal phosphate wasting due to increased production of fibroblast growth factor 23 (FGF23). Chronic hypophosphatemia causes the accumulation of severe musculoskeletal morbidities, and delays in diagnosis are common, which can lead to considerable healthcare resource use (HCRU). The objective of this study is to estimate HCRU from histories of adults with TIO not curable by surgery, prior to enrollment in the UX023T-CL201 burosumab phase 2 trial.

Methods: Histories of the 14 TIO patients enrolled in UX023T-CL201 were assessed independently by two reviewers. Data related to clinical events directly associated with HCRU were extracted and categorized.

Results: Mean age of TIO subjects enrolled in the trial was 56.9 ± 10.3 years (range 33-68); 57% (8) were male. Mean time between first symptoms and TIO diagnosis was 4.2 ± 4.1 years (range 0.1-13.2); mean time since diagnosis was 13.7 ± 13.0 years (range 0.7-35.8). Tumors were identified in 71% (10) patients, with surgical removal attempted in 64% (9).

Subjects underwent a mean of 11.1 ± 13.2 tumor investigations (range 1-46). The most frequent were magnetic resonance imaging (mean 4.9 ± 7.5 per patient; range 0-29), positron emission tomography/computed tomography (mean 1.9 ± 5.3; range 0-20), octreotide scan (mean 1.4 ± 2.3; range 0-7), and computed tomography (mean 1.3 ± 1.8; range 0-5).

All patients had a history of active vitamin D treatment, and 93% (13) had a history of oral phosphate treatment, with a mean duration of 10.4 ± 12.5 (range 0.3-35.0) and 10.5 ± 12.2 years (range 1.2-35.0), respectively.

History of fracture was reported in 93% (13) patients, with a mean of 5.4 ± 6.8 fractures per patient (range 0-28). The most frequently reported fracture locations were the ribs (mean 1.6 ± 3.3 fractures; range 0-13), foot/ankle (mean 1.0 ± 2.1; range 0-8), and femur (mean 0.7 ± 0.9; range 0-2).

Orthopedic procedures included spinal laminectomy in 21% (3) subjects, spinal corpectomy in 14% (2) subjects, and hip and knee arthroplasty in 14% (2) subjects each.

Conclusion: TIO is associated with substantial HCRU resulting from diagnosis, attempted tumor localization/removal, and disease management.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/healthcare-resource-utilization-associated-with-tumor-induced-osteomalacia-review-of-patient-histories-prior-to-entry-in-clinical-trial-ux023t-cl201/