What is Hidden Behind the Numbers? Parathyroid Adenoma or Carcinoma?

Introduction : Significant elevations in parathyroid hormone (PTH) and calcium elevations are commonly observed between parathyroid carcinoma and adenoma.  Clinicians are often taught to suspect carcinoma with PTH and calcium remarkably greater than expected levels in primary hyperparathyroidism. PTH levels in parathyroid cancer are on average 5-10 times the upper limit of normal and >500 mg/dL, while PTH-secreting adenomas typically present within the normal range or as slightly elevated. Corrected calcium is another laboratory value historically noted as significantly elevated in cases of carcinoma vs adenoma, presenting with an average of 14.6-15.0 mg/dL vs 11.1 mg/dL.

Case Description : Case 1: A 24-year-old man was hospitalized with hypercalcemia crisis with mental status changes, calcium of 16.6 mg/dL, and PTH of 1860 pg/mL. A 3.61 x 1.88 x 2.49 cm multi-cystic mass was excised en-bloc with left thyroid lobectomy via central neck dissection. Pathology revealed benign parathyroid adenoma. Case 2: An 86-year-old woman was hospitalized with bacterial pneumonia and incidentally found to have hypercalcemia with calcium of 13.3 mg/dL and PTH of 170 pg/mL. A 1.7 cm inferior right thyroid mass was excised en-bloc with right thyroid lobectomy via central neck dissection. Pathology revealed parathyroid carcinoma.

Discussion : Parathyroid hormone and calcium alone cannot be used to determine malignancy potential in primary hyperparathyroidism. Previously published cases have described significantly elevated PTH and calcium levels in parathyroid carcinoma compared to adenoma. We present two cases with laboratory values that significantly deviate from the expected laboratory values for the respective diagnosis, indicating that these values lack utility in differentiating adenoma from carcinoma. Parathyroid cancer is a rare endocrine malignancy and should be considered as a differential in primary hyperparathyroidism. There are no clinical or biochemical findings that clearly distinguish between parathyroid cancer and adenoma.