Aim
TIO, a paraneoplastic disorder characterised by renal phosphate wasting, is cured by surgical removal of the culprit tumour. Despite correct localization, some refractory to intervention, resulting in substantial complications of long-term medical therapy. We aim to identify risk factors associated with a refractory outcome.
Methods
This is a retrospective cohort of 44 TIO patients diagnosed from 1998 to 2023 who underwent targeted intervention following successfully localization. Cure was defined as maintenance of normophosphatemia without supplementation for >1 month post-localized treatment, maintained at last follow-up.
Results
Median age of diagnosis was 56 years, followed-up over 56.8 months. 29 patients achieved cure and 15 had a refractory outcome. A greater proportion of refractory tumors were localized in the spine (33.3% versus 6.9% in cure group, p=0.023) and in the bone (67% versus 31% in cure group, p=0.024). On univariate cox regression, HR for predicting cure was 3.43 (95% CI 1.45-8.11, p=0.005) for patients diagnosed within the past 10 years (compared to >10 years ago), and that for a negative surgical tumor margin was 2.56 (95% CI 1.20-5.45, p=0.015) compared to positive or unspecified margins. After adjustment for year of diagnosis, a tumor originating from soft tissue (HR 2.72 versus bone, 95% CI 1.22-6.09, p=0.015), located outside the spine (HR 0.22 for spine versus non-spine, 95% CI 0.05-0.96, p=0.043) or in the limbs (HR 2.28, 95% CI 1.05-4.96) had a higher chance 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.
Conclusion
Tumors diagnosed within the past decade and with a clear resection margin had a more favorable prognosis. With regards to tumoral factors, baseline biochemistry was not informative in predicting cure, while bone and/or spine localization of TIO were associated with a refractory outcome.