The parathyroid glands are four tiny glands in the neck near the thyroid gland. The parathyroid glands make parathyroid hormone (PTH), which helps the body use calcium and keeps the amount of calcium in the blood at normal levels.

Tumors in the parathyroid are usually benign (not cancer). These are called adenomas. Fewer than 100 people a year are diagnosed with parathyroid cancer in the United States.

Having certain inherited disorders can increase the risk of parathyroid cancer. These include familial isolated hyperparathyroidism (FIHP) and multiple endocrine neoplasia type 1 (MEN1) syndrome. Having radiation therapy to the neck can increase the risk of benign parathyroid tumors.

With either a benign tumor or cancer, the gland may make too much PTH. This causes hypercalcemia (too much calcium in the blood), which is a serious and life-threatening condition. There may be no signs or symptoms of a parathyroid tumor until there is too much calcium in the blood. Signs and symptoms include weakness and feeling tired. Larger parathyroid tumors may cause a lump in the neck near the thyroid.