Glucagonoma

Definition

The group of tumors that are associated with the hormone-secreting (endocrine) glands of the body.

Description

The glands in the body that make and secrete hormones comprise the endocrine system. All endocrine glands secrete hormones directly into the bloodstream, where they travel to a target organ or cell to trigger a specific reaction. These glands are primarily involved in controlling many of the slow and long-term activities in the body, such as growth, sexual development, and regulation of blood levels for many important proteins and essential chemical elements.

Endocrine glands are found in the head and neck region, the abdominal region, and the pelvic area (the region where the reproductive organs are located). The following are the main endocrine glands of the body:

• Pituitary gland. Found at the base of the brain, this small gland is important because it secretes several hormones that control the activity of other endocrine glands.

• Thyroid gland. Situated in the front of the neck, in the region of the Adam's apple, this gland secretes hormones that regulate body temperature, heart rate, and metabolism.

• Parathyroid glands. These four glands, with a pair on either side of the thyroid gland in the neck region, produce parathyroid hormone, which helps control the level of calcium in the blood.

• Pancreas. Found close to the stomach in the abdominal region, the pancreas contains two groups of cells. One group functions as an exocrine gland, secreting digestive enzymes into the intestines through a duct. The other, known as islets of Langerhans (or islet cells), functions as an endocrine gland and secretes hormones that control blood sugar levels and aid digestion.

• Adrenal glands. These two glands, one located above each kidney, secrete hormones that prevent inflammation and help regulate blood pressure, blood sugar levels, and metabolism.

• Ovary. A woman has two small ovaries in the pelvic area. They contain the egg cells and secrete the hormones progesterone and estrogen. These hormones have many functions, including controlling the onset of puberty, the timing of menstruation, and the changes associated with pregnancy.

• Testis (also called testicle). Men typically have two testes located outside the body in the lower pelvic area. They produce sperm and the hormone testosterone, which signals the onset of puberty, maintains the expression of male characteristics, such as facial hair, and stimulates sperm production.

Endocrine system tumors are rare. Although certain types are likely to be diagnosed as malignant (cancerous), endocrine tumors are often noncancerous (benign). Each year endocrine system cancers account for only around 4% of all new cancer cases in the United States. In 2001, it is expected that 53,460 Americans will develop an endocrine system cancer, resulting in an estimated 16,600 deaths.

The most common cancers of the endocrine system are ovarian cancer and thyroid cancer. Ovarian cancer represents about 44% of all endocrine system cancers and affects eight out of every 100,000 American women. New cases of ovarian cancer in 2001 will likely reach over 23,000, and nearly 13,000 will die from the disease. Roughly six out of every 100,000 Americans develop thyroid cancer, which accounts for 36% of all endocrine system cancers. It is estimated that 19,000 new cases will be diagnosed in 2001 and result in 1,300 deaths. Other malignant endocrine tumors are much rarer. Testicular cancer affects about two out of every 100,000 American men, while the remaining cancer types combined affect roughly one out of every 100,000 Americans.

Many benign and malignant endocrine tumors are treatable with a combination of surgery and medication, and the survival rates for many endocrine cancers is good. Two exceptions are ovarian cancer and adrenocortical carcinoma, a tumor of the adrenal gland. About 50% of ovarian cancer patients and 40% of those diagnosed with an adrenocortical carcinoma will survive five years or more after the initial diagnosis. These cancers have poor survival rates because they are usually first diagnosed after they have spread or reached an advanced stage. Among the different cancers, thyroid cancer and testicular cancer have some of the better 5-year survival rates; both approach 95%.

Symptoms of many endocrine tumors are associated with the excessive secretion of hormones. Hormone-producing tumors are called functional tumors, while those that do not secrete hormones are called nonfunctional tumors. Both types are potentially malignant.

Types of cancers

Proceeding from the head region to the pelvic area, endocrine system tumors include:

• Pituitary tumors. These tumors are classified by the type of hormone they secrete. They are rarely malignant but can cause heath problems, including visual complications. One type of tumor results in Cushing's syndrome.

• Thyroid tumors. Only 5% of the tumors found on the thyroid are malignant. A malignant tumor can indicate one of the four types of thyroid cancer.

• Parathyroid tumors. Around 5% are malignant and result in a diagnosis of parathyroid cancer. Overproduction of parathyroid hormone, a condition known as hyperparathyroidism, is a common condition associated with both benign and malignant tumors. Untreated, hyperparathyroidism can result in osteoporosis (bones become brittle and fracture easily), kidney stones, peptic ulcers, and nervous system problems.

• Endocrine pancreatic tumors. Benign and malignant tumors are often treatable with surgery. Malignant tumors are rare. The most common types of tumors are a gastrinoma, which is associated with Zollinger-Ellison syndrome, insulinoma, and glucagonoma.

• Adrenal tumors. One type of tumor, a pheochromocytoma, is found on the inner part of the adrenal gland (the adrenal medulla). About 10% are malignant. An adrenocortical carcinoma is a malignant tumor on the outer part of the gland (adrenal cortex), and a common symptom is the occurrence of Cushing's syndrome. Both tumors are very rare.

• Ovarian tumors. Tumors can develop in the egg cells inside the ovary (germ cell tumors), but most occur in the cells lining the outside of the ovary, and most of these tumors are benign.

• Testicular tumors. Tumors can occur in one or both of the testes. Over 90% develop in the germ cells and only 4% involve the endocrine cells of the testes.

• Multiple endocrine gland tumors. Some disorders result in the simultaneous occurrence of tumors on several endocrine glands. Many of these are inherited disorders, including multiple endocrine neoplasia syndromes, von Hippel-Lindau syndrome, and von Recklinghausen's neurofibromatosis.

Pituitary tumorsThyroid tumorsParathyroid tumorsEndocrine pancreatic tumors, including gastrinoma, insulinoma, and glucagonomaAdrenal tumors, including pheochromocytoma and adrenocortical carcinomaOvarian tumorsTesticular tumorsMultiple endocrine gland tumors (tumors on several endocrine glands at once)

KEY TERMS

Endocrine gland

Any gland that makes hormones and secretes them directly into the bloodstream.

Exocrine gland

Any gland that secretes substances outward through a duct into a body cavity or onto a body surface (e.g., sweat glands and salivary glands).

Germ cell

Any cell in the body that eventually produces either a mature egg cell (female) or a mature sperm cell (male).

Inherited disorder

A disease that has a tendency to occur within a family. A disorder may be acquired due to a gene or genes that are passed from parent to child.