In this article, I will discuss ectopic secretion of hormones by malignant tumours in the body. The most important ectopic hormone secretion is due to Cushing syndrome and the syndrome of inappropriate antidiuretic hormone in addition to hypercalcemia.
Usually Cushing syndrome is caused due to an adenoma of the adrenal cortex which oversecretes the hormone cortisol. In addition, administration of cortisol analogues can develop in affected individuals Cushing syndrome symptoms such as obesity and diabetes.
Also, Cushing syndrome can be caused due to carcinoma of the adrenal cortex which can oversecretes the hormone cortisol. In addition, hyperplasia of the adrenal cortex as a result of increased secretion of adrenocorticotropic hormone (ACTH) by the anterior pituitary gland can cause increased secretion of cortisol by the hyperplastic cells of the adrenal cortex.
ACTH has a direct stimulatory effect on cortisol synthesis and secretion by the adrenal gland. Certain malignant tumours in the body can secrete this hormone in ectopic fashion. Namely, it is not secreted by its usual source but by a tumour that can affect the body. This is especially notable in small cells bronchial carcinoma of the lung tissue.
The excessive secretion of ACTH stimulates the secretion of cortisol by the cortex of the adrenal gland which can cause hyperplasia of this gland in its cortical area. The excessive secretion of cortisol in turn by the neoplastic tumour can cause Cushing syndrome symptoms such as diabetes and hyperglycemia in addition to elevation of the blood pressure in affected individuals.
ACTH is a polypeptide hormone in contrast to cortisol which is a steroid hormone. ACTH is usually secreted by the anterior pituitary gland.
The other important hormone which has significance in ectopic secretion by neoplastic tumours in the body is called antidiuretic hormone. This hormone is usually secreted by the posterior pituitary gland in response to hypovolemia or due to plasma hyperosmolality. It functions by stimulating the kidney to conserve water in the nephron tubules.
There are usually two disorders of this hormone. These are disorder of increased secretion and disorder of decreased secretion. This hormone is the one that regulates the level of water in the body along with two other hormones that are called atrial natriuretic hormone and aldosterone.
Usually increased secretion of the antidiuretic hormone by the posterior pituitary gland is caused due to several reasons causing retention of water in the body with concentrated urine. Among the conditions that can cause increased secretion of the antidiuretic hormone include pulmonary diseases such as tuberculosis and pneumonia. In addition brain neoplasms can also cause increased secretion of this hormone.
Drugs that usually function as agonists to this hormone can amplify its effect of water retention. In addition, liver cirrhosis and addison disease and hypothyroidism can also cause increased secretion of this hormone. Tumours that are unrelated to this hormone but which secretes it ectopically include carcinoma of the lung causing dilutional hyponatremia. Other neoplasms that can secrete this hormone ectopically include the carcinoid syndrome and pancreatic adenocarcinoma.
Hypercalcemia is the third type of disorder that can be caused due to ectopic hormone secretion. Hypercalcemia can be caused due to a neoplastic tumour Also. Usually these neoplastic tumours secrete analogues to parathyroid hormone causing excessive resorption of calcium ions from the bone tissue by stimulating the bone cells which are called osteoclasts. Also dissolution of calcium from bones can occur due to metastasis of other tumours to the bone tissue.