Causes of Adrenal Tumors
As with other types of cancer, the causes of adrenal gland tumors are not well understood. In companion dogs, adrenal tumors are split fairly equally between adenomas, which are benign or non-malignant masses, and adenocarcinomas, which are malignant. A malignant tumor is one that tends to progressively worsen with time and, if not treated or removed, usually will result in death of the affected animal. Malignant masses typically are highly invasive, meaning nearby tissue is affected, and metastatic, which means that the cancerous cells spread from one part of the body to others.
Adenomas can be either functional or non-functional. Non-functional adenomas do not affect the production or release of adrenal steroid hormones. However, functional adenomas, and almost all adenocarcinomas, stimulate unregulated release of corticosteroids from the adrenal cortex – most commonly cortisol, a glucocorticoid hormone. They can cause over-production of other steroids, as well. Functional tumors cause the adrenal glands to keep releasing adrenal hormones regardless of the presence or absence of normal pituitary gland adrenocorticotropic hormone (ACTH) stimulus and regulation. Functional adrenal tumors basically keep the affected gland or glands “turned on” all the time, as they are constantly being bombarded with copious amounts of ACTH. The unregulated overabundance of corticosteroids in circulation is a condition called hyperadrenocorticism, also commonly known as “Cushing’s Disease.”
Functional adenomas and/or adenocarcinomas can develop on one or both of the adrenal glands. In dogs, the right and left adrenal glands seem to be affected by both types of adrenal tumors with equal frequency. When a functional mass affects only one of the glands, the other – referred to as the “contralateral” adrenal gland - starts to shrivel and decreases dramatically in size. This happens because the overload of circulating corticosteroids from the functional tumor signals the pituitary gland to stop releasing ACTH. This, in turn, shuts down the cortex of the contralateral adrenal gland, leaving it with nothing to do. It basically withers away from disuse.
Prevention of Adrenal Tumors
Veterinary science does not yet fully understand the causes of adrenal gland adenomas and adenocarcinomas. As a result, there is no realistic way to describe a sound preventative protocol.
Adenocarcinomas are much more serious even than functional adenomas, because they are malignant and prone to be progressive, highly invasive and metastatic. When an adrenal tumor is suspected, most general practitioners will refer the owner and her dog to a veterinary teaching hospital or other highly-specialized referral center, where the newest and most advanced diagnostic and treatment options are available.