What are pheochromocytomas? Pheochromocytomas are very rare tumors of chromaffin cells, which are cells of the adrenal gland that make hormones called catecholamines. In pheochromocytoma, the cells overproduce catchecholamines, specifically norpinephrine, epinephrine (also known as adrenaline), and dopamine, all of which are necessary for our bodies to function. Pheochromocytomas are found in the adrenal glands; humans have two adrenals, and each sits on top of a kidney. Generally, only one adrenal gland, not both, is affected by a pheochromocytoma, but there may be multiple tumors in that gland. Tumors that are found outside the adrenal glands (less than 10% of cases) are known as extra-adrenal pheochromocytomas or paragangliomas. Most tumors that start in the chromaffin cells do not spread to other parts of the body and are not cancer, but are benign tumors. A small percent of ... read more on Pheochromocytoma: The Basics