Biochemical and Structural Response to Lenvatinib in Metastatic Parathyroid Carcinoma: Case Report.

Parathyroid carcinoma (PC) is an exceptionally rare endocrine malignancy characterized by severe hypercalcemia and high recurrence rates. We present the case of a 34-year-old male with chronic kidney disease who developed pathological fractures and progressive pulmonary metastases secondary to PC. Genetic analysis revealed a pathogenic variant in the CDC73 gene, indicating a hereditary predisposition. Following surgical resection, the patient experienced early biochemical relapse. Initial management with bisphosphonates, denosumab, and cinacalcet achieved temporary control of hypercalcemia. Upon radiological progression, lenvatinib therapy was initiated, resulting in 9 months of biochemical control and stabilization of both local disease and pulmonary metastases. However, discontinuation of denosumab and cinacalcet due to limited access led to a relapse of severe hypercalcemia and disease progression, necessitating the cessation of lenvatinib and transition to palliative care. This case underscores the diagnostic and therapeutic challenges of PC, highlights the potential role of targeted therapies like lenvatinib in advanced disease, and emphasizes the critical importance of sustained access to essential treatments.