Hypercalcemia Of Malignancy

Recently we discussed primary hyperparathyroidism (click here to read that post) in dogs and its effect on calcium management in the bloodstream.

Laddie’s anal sac tumor is producing PTHRP and driving his calcium very high. In addition, he has metastasis to his sublumbar lymph nodes.

However, hypercalcemia in dogs is more likely to occur in neoplasia (cancer) located in non-parathyroid sites in the body. It is then termed hypercalcemia of malignancy and/or pseudohyperparathyroidism. The three most common types of cancer likely to cause hypercalcemia in the dog are:
• lymphoma/leukemia (cancer of the lymphatic system of the body, part of the immune system)
anal sac adenocarcinoma
• multiple myeloma, a protein-producing cancer of plasma cells, a type of white blood cell (WBC), also part of the immune system.

All of these cancers have the ability to secrete a variety of ingredients, one of which is parathyroid hormone-related protein (PTHRP) that mimic parathyroid hormone, causing the body to mobilize calcium from the bones, reabsorb calcium from the urine and absorb more calcium from food in the intestine. Bone activity accounts for most of the excess calcium in the bloodstream. PTHRP can actually be quantitatively measured in the bloodstream.

The dots in this radiograph outline the cancer in the sublumbar lymph nodes. Eventually, this mass can grow to the point that it interferes with colon and bladder function.

Hypercalcemia is a concern because of its widespread damage of body systems. Kidneys can be impaired physically and functionally. Calcification (mineralization) of various soft tissue body parts is also common, including skin and internal organs. Renal failure (click here to read about kidney failure) often ensues, causing the patient to drink (and thus urinate) excessively, eventually losing his appetite and resulting in vomiting and death.

In lymphoma and leukemia, treatment of the disease process often temporarily reduces hypercalcemia.

In both primary-site and metastatic anal sac adenosarcoma, surgical removal or “debulking” of cancerous masses can reduce hypercalcemia dramatically. Cure of this type of cancer is uncommon.
See you next week, Dr. Randolph.

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