Hypercalcemia occurring in patients with advanced breast cancer (BC) is generally due to osteolytic metastases or to the activity of circulating tumor-derived products. In these conditions, the production of endogenous PTH is reduced. The frequency of hypercalcemia due to primary hyperparathyroidism in breast cancer is unknown. We examined the occurrence of primary hyperparathyroidism in a large group of women with treated BC. A total of 100 consecutive women aged 28-80 years with treated breast cancer were enrolled. One hundred and two healthy age-matched women and 60 age-matched female patients with differentiated thyroid carcinoma examined before thyroidectomy were used as controls. Intact serum PTH and serum calcium were measured in all patients and controls. Hypercalcemia associated with elevated serum PTH concentration indicating primary hyperparathyroidism was found in 7 BC patients (7%) and in none of healthy women or patients with thyroid cancer. The pre-operative staging of BC patients with primary hyperparathyroidism was I in six and II in one of them, and no patient had evidence of distant metastases. A parathyroid adenoma was found in all 6 BC patients submitted to neck exploration, one patient refused surgery. Serum calcium and PTH concentrations returned to normal levels after surgery. Two BC patients had increased serum PTH and normal calcium concentrations. One of them had low serum 25-hydroxyvitamin D [25(OH)D]. One patient with spread bone metastases had neoplastic hypercalcemia with undetectable serum PTH concentration. All remaining 90 BC patients had serum calcium and PTH concentrations within normal limits, but their mean (+/- SD) values (9.6 +/-0.5 mg/dl for serum calcium, 38.0 +/- 16.4 mg/dl for serum PTH) were slightly but significantly greater than in normal controls (9.3 +/-0.5 mg/dl, p=0.003 and 27.9 +/- 10.6 pg/ml, p=0.0001, respectively) and in patients with thyroid cancer (9.2 +/-0.6 mg/dl, p=0.001 and 26.2 +/- 11.0 pg/ml, p=0.001), with no relationship with clinical staging or anti-tumor therapy. In conclusion: 1) an increased frequency of parathyroid adenoma was found in BC patients with mildly aggressive neoplastic disease; 2) in BC patients with no evidence of primary hyperparathyroidism mean serum PTH and calcium concentrations were significantly greater than in healthy controls and in patients with thyroid carcinoma; and 3) this finding was unrelated to clinical staging or anti-tumor therapy. Thus, primary hyperparathyroidism should be considered as a possible cause of hypercalcemia in patients with non-aggressive breast cancer. We suggest that serum PTH should be determined in all BC patients with increased serum calcium concentration, especially in those with no evidence of metastatic disease.
