Parathyroid carcinoma diagnosed after pulmonary metastases 8 years after initial parathyroidectomy

Parathyroid carcinoma is a rare form of cancer. We describe a 45-year-old man diagnosed with parathyroid carcinoma long after initial surgery. At age 24, the patient had elevated serum calcium and intact parathyroid hormone (PTH). Ultrasonography revealed a left lower parathyroid tumor, which led to the diagnosis of primary hyperparathyroidism. Parathyroidectomy was performed, and the pathological diagnosis was parathyroid adenoma. At age 32, hypercalcemia and elevated intact PTH recurred, and computed tomography revealed a right lung tumor with focal uptake on ^99mTc-methoxyisobutylisonitrile scintigraphy, which was clinically diagnosed as probable pulmonary metastasis from a parathyroid neoplasm; however, the patient declined further evaluation. At age 45, progressive hyperparathyroidism and enlargement of the right lung tumor were identified, leading to thoracoscopic resection. The resected tumor showed histopathological features similar to those of the previously resected parathyroid tumor. Immunohistochemistry revealed a low Ki-67 index but complete loss of nuclear parafibromin expression, confirming metastatic parathyroid carcinoma. Seven years after surgery, there was no evidence of recurrence or metastasis. Because it is often difficult to differentiate parathyroid carcinoma from parathyroid adenoma, and recurrence or metastasis may occur after a long interval, the possibility of carcinoma should always be considered and long-term follow-up is essential.