The case of hypercalcemia secondary to metastasis to a benign parathyroid adenoma is reported. The patient had documented lung adenocarcinoma with multiple bone metastases and a mass in the lower anterior neck for at least 5 months before hypercalcemia and hypophosphatemia resistant to treatment developed. Autopsy revealed widespread metastatic disease including metastatic tumor invading a benign parathyroid adenoma. The analysis of four cases of metastatic cancer spread to a benign parathyroid adenoma reported previously revealed that two of them also had hypercalcemia during a late stage of the disease. There are data that the incidence of metastases to parathyroid gland might be as high as 11.9%, and the incidence of parathyroid adenomas in patients with cancer is significantly higher than in controls. The metastases to benign parathyroid adenomas might be another mechanism of hypercalcemia of malignancy.

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