Parathyroid carcinoma

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Histological appearance of a parathyroid carcinoma showing marked anisokaryosis and anisocytosis[1]

Parathyroid carcinoma is a rare neoplasm of the canine parathyroid gland.

Because of the close anatomical location to the thyroid gland, invasion of the thyroid may occur, though rarely reported.

Because of the intimate involvement of calcium regulation employed by the parathyroid gland (produces parathyroid hormone), calcium homeostasis is disrupted by excessive synthesis and secretion of parathyroid hormone, resulting in clinical hyperparathyroidism and hypercalcemia (normal range 1.91 - 3.03 mmol/L) are commonly observed in affected dogs[2][3].

In primary hyperparathyroidism, the most common tumors of the parathyroid glands are adenomas, whereas hyperplasia and parathyroid carcinoma are more infrequently diagnosed[4][5].

Diagnosis is based on presence of a palpable parathyroid mass and ultrasonographic confirmation of neoplastic appearance to the mass.

Serum levels of both parathyroid hormone and parathyroid hormone-related protein should be assessed as levels may fluctuate with not only parathyroid carcinoma with with other non-parathyroid malignancies[6]

Fine needle biopsy and histological analysis of sample tissues is usually definitive. Histologically, these tumors present with indistinct cell borders, high nuclear-cytoplasmic, high mitotic index and moderate anisokaryosis and anisocytosis, with occasional binucleated cells and megalocytes[1].

A differential diagnosis would include hyperparathyroidism, parathyroid adenoma, parathyroid hyperplasia[7], hypercalcemia of malignancy (anal sac adenocarcinoma, multiple myeloma and osteosarcoma), chronic renal disease, hypoadrenocorticism and vitamin D toxicosis.

Parathyroidectomy is usually curative although hypocalcemia is a common post-operative complication requiring calcium and vitamin D supplementation. In some cases postsurgical rehabilitation of c

Recurrences or metastases are very rare[8].


  1. 1.0 1.1 Sakals SA et al (2010) Diagnosing the etiology of hypercalcemia in a dog: a case of primary hyperparathyroidism. Vet Pathol 47(3):579-581
  2. Sakals S et al (2006) Determining the cause of hypercalcemia in a dog. Can Vet J 47(8):819-821
  3. van Vonderen IK et al (2003) Parathyroid hormone immunohistochemistry in dogs with primary and secondary hyperparathyroidism: the question of adenoma and primary hyperplasia. J Comp Pathol 129(1):61-69
  4. Berger B & Feldman EC (1987) Primary hyperparathyroidism in dogs: 21 cases (1976–1986). J Am Vet Med Assoc 191:350–356
  5. Schenck PA & Chew DJ (2008) Hypercalcemia: a quick reference. Vet Clin North Am Small Anim Pract 38:449–453
  6. Mellanby RJ et al (2006) Plasma concentrations of parathyroid hormone-related protein in dogs with potential disorders of calcium metabolism. Vet Rec 159(25):833-838
  7. Jores K & Kessler M (2011) Primary hyperparathyroidism in the dog. Diagnosis, therapy and postoperative management in 19 dogs. Tierarztl Prax Ausg K Kleintiere Heimtiere 39(6):389-396
  8. Sawyer ES et al (2012) Outcome of 19 dogs with parathyroid carcinoma after surgical excision. Vet Comp Oncol 10(1):57-64