Prognostic factors for refractory outcome in localizing TIO: experience in a tertiary center.

Context: TIO, a paraneoplastic disorder characterised by renal phosphate wasting, is cured by surgical removal of the culprit tumour. Despite correct localization, some remain refractory to intervention, resulting in substantial long-term medical complications.

Aim: We aim to identify risk factors associated with a refractory outcome.

Methods: This is a retrospective cohort of 44 TIO patients diagnosed from 1998-2023 who underwent targeted intervention following successfully localization. Cure was defined as maintenance of normophosphatemia without supplementation for >1 month, maintained at last follow-up.

Results: 29 patients achieved cure and 15 had a refractory outcome. On univariate cox regression, HR for predicting cure was 3.43 (95%CI 1.45-8.11, p=0.005) for patients diagnosed after 2013 (compared to before), and that for a negative surgical tumor margin was 2.56 (95%CI 1.20-5.45, p=0.015) compared to positive/unspecified margins. After adjustment for year of diagnosis, tumors originating from soft tissue (HR 2.72 versus bone, 95%CI 1.22-6.09, p=0.015) or located outside the spine (HR 0.22 for spine versus non-spine, 95%CI 0.05-0.96, p=0.043) had higher chances of cure. Size of tumor, age, gender, or baseline biochemistry including levels of FGF23, phosphorus, 1,25(OH)2D or ALP were not predictive of cure. Post-procedural FGF23 was the best biochemical marker of cure (AUC 0.899, 95%CI 0.764-1.00, p < 0.001).

Conclusion: Tumors diagnosed within the past decade with clear resection margins had more favorable prognoses. With regards to tumoral factors, baseline biochemistry was uninformative in predicting cure, while bone and/or spine localizations were associated with a refractory outcome.