A tumor characterized by the presence of hormone-producing cells is referred to as an APUD (amine precursor uptake and decarboxylation) tumor. These APUD cells are found in different regions of the body.
APUD cell tumors can occur in various glands and organs, including the thyroid gland, pancreas, and lungs. Carcinoid tumors, which develop in the intestine or lung (see carcinoid syndrome), as well as phaeochromocytoma, a specific type of adrenal tumor, also fall under the category of APUD cell tumors.