Objective: Involvement of the parathyroid glands by metastatic tumor is rare. Breast is 1 of the primary sites in metastatic cancers. We introduce a rare case of metastatic breast carcinoma affecting a parathyroid gland, which was clinically combined with parathyroid gland hyperplasia.
Case report: A 65-year-old woman was referred due to hypercalcemia and constipation. The patient had a history of left breast carcinoma. She was admitted to the hospital because of the recent discovery of hypercalcemia and elevation of PTH. A Tc99m-sestamibi scan showed retained uptake in the right thyroid and in the lower pole of the left thyroid gland. Aspiration biopsy results revealed that the nodule in the posterior portion of the right thyroid was metastatic breast cancer and the nodule in the left thyroid gland was the hyperplastic parathyroid gland.
Conclusion: This case illustrates that hyperparathyroidism caused by parathyroid hyperplasia was concurrent with metastatic breast cancer to a parathyroid gland without disseminated systemic metastasis. Although this case is very uncommon and it is not clear whether there is a relationship between breast cancer and primary hyperparathyroidism, that possibility should always be considered as the cause of hypercalcemia in patients with breast cancer.