Parathyroid adenoma-related hypercalcaemia in breast cancer: a critical diagnosis in clinical oncology.

Hypercalcaemia in patients with breast cancer is generally due to osteolytic metastases or to the activity of circulating tumour-derived products. Hyperparathyroidism is one of the most frequent aetiological factors in benign hypercalcaemia, but it is usually not considered in oncology patients. We present a high-risk early breast cancer case with hypercalcaemia in the 19th postoperative month of follow-up. The patient had high serum parathyroid hormone (PTH) levels, but ultrasonography was not diagnostic, and the existence of parathyroid adenoma was established by scintigraphy. Histopathological examination revealed chief cell parathyroid adenoma. The patient is still free of cancer recurrence in the 48th month of follow-up. Hyperparathyroidism should be considered as a possible cause of hypercalcaemia in breast cancer patients, and parathyroid scintigraphy is essential in the initial evaluation of the cases with increased serum calcium and PTH concentrations.