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A pheochromocytoma (also phaeochromocytoma, English spelling) is a tumor in the medulla of the adrenal glands (or, rarely, the ganglia of the sympathetic nervous system) which secretes excessive amounts of catecholamines, usually epinephrine and norepinephrine.

Pheochromocytomae occur most often during young-adult to mid-adult life. Less than 10% of pheochromocytomas are malignant (cancerous).

These tumors can form a pattern with other endocrine gland cancers which is labelled multiple endocrine neoplasia. Pheochromocytoma is listed within the groups MEN 2a and MEN 2b.