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Canine Pheochromocytoma

Pheochromocytoma is a special type of endocrine tumor that arises from the adrenal gland. The cells that give rise to this specific tumor secrete certain hormones that regulate various functions within the body. Tumors typically occur in middle-aged to older dogs. Many cases may have the tumors diagnosed incidentally, but up to half of the dogs have signs/symptoms present. These signs and symptoms include appetite loss, weight loss, panting, lethargy, collapse, elevated heart rate and high blood pressure.

Many of the tumors are locally invasive into regional tissue and surrounding blood vessels. Sometimes the tumors rupture a lead to pale gums, abdominal distention, and collapse. Tumor spread (metastasis) occurs in 20-30% of dogs. Tumors may be detected with abdominal ultrasound or other imaging modalities, but a biopsy is necessary to achieve a diagnosis.

Treatment largely centers around surgery to remove the tumor. In cases where the entire tumor cannot be removed, post-op chemotherapy is recommended. Unfortunately, pheochromocytomas are poorly responsive to traditional chemotherapy agents due to resistance mechanisms inherently present within the cells. The use of newer chemo agents such as Palladia and Kinavet may be considered as these types of chemotherapeutics may overcome certain types of drug resistance. Other forms of therapy include low dose treatment (metronomic therapy) designed to prevent blood vessel growth and tumor enlargement. Chemo and metronomic therapy have limited statistical information regarding the outcome.

The prognosis is variable and often predicted based on the local tumor aggressiveness, ability to surgically remove the tumor, and malignant features that may or may not be present on biopsy. In the cases where tumors are non-invasive and complete surgical removal is possible, the survival time is generally years and some patients may be considered ‘cured’ following surgery. In other cases, surgery will reduce the signs/symptoms associated with the tumor (see above) and provide a better quality of life for a patient. If the tumors are invasive, ruptured, high grade or advanced, or inoperable, the prognosis is more guarded and the survival time may only be a few months.