Double Parathyroid Carcinoma Associated With CDC73 Mutation: A Rare Case.

Primary hyperparathyroidism is a relatively common endocrine disorder, but its malignant form is extremely rare and often presents diagnostic and therapeutic challenges. We present an unusual case involving a man in his late 40s who presented with progressive musculoskeletal pain, functional decline, and weight loss. Laboratory tests revealed severe hypercalcemia and markedly elevated parathyroid hormone levels. Imaging identified multiple osteolytic lesions, and biopsy confirmed osteitis fibrosa cystica. Cervical imaging revealed two suspicious parathyroid nodules, raising concern for malignancy. The patient underwent en bloc resection of the left parathyroid and hemithyroidectomy, followed by right inferior parathyroidectomy and left central compartment lymphadenectomy. Histopathological analysis confirmed parathyroid carcinoma with thyroid invasion on the left and an atypical neoplasm on the right, although capsular invasion could not be assessed. Postoperatively, the patient developed hungry bone syndrome, requiring calcium and vitamin D supplementation. Genetic testing revealed a CDC73 mutation, confirming the genetic basis of the disease.