A rare, genetic disorder marked by tumors called paragangliomas, which are found in paraganglia. Paraganglia are groups of nerve-like cells found near the adrenal glands and near blood vessels or nerves in the head, neck, chest, abdomen, and pelvis. Paragangliomas that form in the adrenal glands are called pheochromocytomas. Paragangliomas are usually benign (not cancer), but sometimes become malignant (cancerous). People with hereditary paraganglioma-pheochromocytoma syndrome usually have more than one paraganglioma, and may have an increased risk of certain types of cancer, such as kidney cancer and thyroid cancer.