How can tumors in endocrine glands cause hormone overproduction?

Tumors in endocrine glands cause hormone overproduction primarily because they are largely autonomous, meaning they are insensitive to the negative feedback control mechanisms that normally regulate hormone levels. While most endocrine tumors are benign adenomas, some are malignant carcinomas that can invade adjacent structures and metastasize.1

Tumors contribute to hormone overproduction through several mechanisms:

• Direct Secretion: Endocrine tumors may produce excessive quantities of the hormone normally secreted by the gland from which they originate.1
• Secondary Hyperplasia: Small, otherwise innocuous endocrine tumors can secrete excessive amounts of a stimulatory hormone, which then causes secondary hyperplasia (an increase in the number of cells) in a target gland, leading to further hormone overproduction. A classic example is a pituitary tumor producing excess adrenocorticotropin, which causes the adrenal glands to become hyperfunctional.1
• Ectopic Production: Some tumors, including those arising from tissues that do not normally have endocrine function (such as lung cancer), can synthesize and secrete hormones, a process known as ectopic hormone production.12
• Multiple Endocrine Neoplasia (MEN): In this hereditary syndrome, patients have genetic mutations that predispose them to the development of tumors in several endocrine glands.12