Hyperparathyroidism in a Large Cohort of Chinese Patients With Tumor-induced Osteomalacia

Context Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by excessive production of fibroblast growth factor 23 (FGF23) by a tumor. Hyperparathyroidism (HPT) including secondary HPT (SHPT) and tertiary HPT (THPT) in TIO patients, which is believed to be associated with phosphate supplementation, has not been well documented. Objectives To clarify the prevalence, clinical characteristics, and risk factors for HPT in a large cohort of Chinese patients with TIO in our hospital. Design, setting, and participants This retrospective study enrolled 202 patients with TIO. Main outcome measurements Occurrence of HPT in patients with TIO. Results HPT was observed in 91 patients (91/202, 45.1%): 84 patients (41.6%) with SHPT and 7 patients (3.5%) with THPT. All patients with THPT underwent parathyroidectomy and only 1 patient experienced recurrence. Compared with patients without HPT, patients with SHPT had longer disease duration, higher rate of phosphate and calcitriol supplementation, lower serum calcium, lower urine calcium excretion, and higher urine phosphate excretion. Compared with patients with SHPT, patients with THPT had even longer disease duration and a higher rate of phosphate and calcitriol supplementation. PTH levels showed positive correlation with intact FGF23 and 1,25-dihydroxyvitamin D levels, but not 25-hydroxy vitamin D level in patients with TIO. Multivariate logistic regression analysis showed that long disease duration and phosphate supplementation were independently associated with occurrence of HPT in patients with TIO. Further logistic regression analysis and restricted cubic spline model revealed dose-response relationship between cumulative dose of phosphate supplementation and PTH levels. Conclusions HPT is common in patients with TIO. To avoid the occurrence of HPT in patients with TIO, timely diagnosis and tumor resection is necessary and an excessive dose of phosphate supplementation is not suggested before surgery.