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Pheochromocytoma is a rare tumor of adrenal gland tissue. It results in the release of too much epinephrine and norepinephrine, hormones that control heart rate, metabolism, and blood pressure .

Causes, incidence, and risk factors

Pheochromocytoma may occur as a single tumor or as more than one growth. It usually develops in the center (medulla) of one or both adrenal glands. Rarely, this kind of tumor occurs outside the adrenal gland, usually somewhere else in the abdomen.

Very few pheochromocytomas are cancerous.

The tumors may occur at any age, but they are most common from early to mid-adulthood.






Reference:
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001380/