Paraneoplastic Hyperthyroidism in Advanced Testicular Non-Seminomatous Germ Cell Tumors: Prevalence and Clinical Management

Introduction: Paraneoplastic hyperthyroidism (PH) has been reported in patients with testicular germ cell tumors (GCTs), sporadically. This disorder is caused by extremely elevated serum levels of beta-human chorionic gonadotropin (bHCG). To date, little is known about the prevalence of PH, and its clinical features are poorly understood. The aim of the present study was to analyze the relative frequency and clinical features of PH in GCTs and evaluate their effects on therapeutic outcomes. Methods: A cohort of 438 patients treated for testicular GCT from 2017 to 2023 was retrospectively analyzed for histology, age, clinical stage, and presence of PH. The clinical features of the patients with PH were evaluated descriptively. The relative frequency of PH was compared among the subgroups using descriptive statistical methods. Results: Three patients with PH were identified; all had clinical symptoms of hyperthyroidism, suppressed serum levels of thyroid-stimulating hormone (TSH), and increased levels of tri-iodothyronin (fT3). All the patients had advanced, metastasized, and non-seminomatous GCTs. Serum bHCG levels ranged from 225,00 U/L to 1,520,000 U/L. The prevalence of PH was 0.7% in the entire GCT population and 60% in those with very high bHCG serum levels. All the patients received standard cisplatin-based chemotherapy along with thyrostatic treatment. The clinical symptoms of the hyperthyroidism rapidly disappeared. TSH levels normalized with decreasing bHCG levels. The PH treatment did not affect the therapeutic outcomes of the patients. Conclusion: PH may occur in 0.7% of all patients with GCT but may be present in up to 60% of patients with very high levels of bHCG. Measuring serum levels of TSH and fT3 should be performed in addition to routine diagnostic measures in all patients with poor prognosis GCTs. Thyrostatic medication is recommended for patients with the clinical symptoms of hyperthyroidism. Early recognition of hyperthyroidism and prompt intervention will reduce comorbidity and help optimize therapeutic outcomes.