Carcinoid Tumors

A tumor, in general, is an overproduction or an abnormal production of cells. A carcinoid tumor is a slow growing tumor, which is a result of an overproduction of hormone-producing cells. These hormone-produc-ing cells are called enterochromaffin cells. Carcinoid tumors are a type of neuroendocrine tumor, and are the most common type of tumor within the neuroendocrine tumor category.

Carcinoid tumors usually originate in the small intestine, and more specifically in the ileum. These types of tumors can be either malignant or benign. In general, the potential for spread and metastasis to the liver increases if the tumor is over two centimeters in diameter. It generally takes three to five years for a carcinoid tumor to grow two centimeters, and in some cases takes up to 10 years. These tumors are not restricted only to the small intestine, but can also occur in places such as the lungs, pancreas, ovaries, or testes.

Because these tumors are derived from hormone-producing cells, the tumor secretes substances that are very similar to hormones such as prostaglandins, histamine, bradykinin, and serotonin. Generally these hormone-like substances do not reach the systemic circulation unless there has been hepatic metastasis. This is due to the fact that if there is no liver involvement, systemic effects will not be seen because a normally functioning, unaffected liver breaks down the excess hormones produced by the tumor. If, however, there has been an excess level of hormones systemically circulating, it can lead to a patient having symptoms that are known as the carcinoid syndrome. About 10 percent of people who have carcinoid tumors will develop carcinoid syndrome. There are a set of clinical features that this syndrome entails: small-bowel obstruction secondary to the tumor; flushing, wheezing, diarrhea, cardiac involvement leading to heart failure and facial telangiectasia; and secondary to hepatic metastases it can cause pain, hepatomegaly, and jaundice.

[Page 345]Within the body, carcinoid tumors would most likely be present growing deep within the mucosa of the organ, and may even be extending into the submucosa underneath. Specifically within the small intestines, carcinoid tumors will often be seen as small nodules growing into the lumen. The tumors will appear brown or yellow, and this is due to the cholesterol and lipid accumulation that is occurring within the tumor. Under a microscope, histologically speaking, carcinoid tumors can be divided into five patterns. The most common type of pattern that has been identified is a combination of the five patterns. Diagnosing a carcinoid tumor can vary depending on the situation. If the tumor is nonfunctioning, as in it is not producing much hormone, then there may be a delay between the actual diagnosis and the onset of symptoms.

According to the Carcinoid Cancer Foundation, these nonfunctional tumors can cause a sequence of events such as intermittent abdominal pain, which leads to a change in bowel habits that can lead to intestinal obstruction. In other cases, however, symptoms will not be present until the tumor has metastasized to the liver. This leads to liver enlargement, which causes abdominal pain. If the tumor is a functioning type of tumor, it is easier to diagnose due to the presence of the carcinoid syndrome and accompanying symptoms. Normally when trying to diagnose a carcinoid tumor, the tests completed are urine 5HIAA, serum serotonin, Neuron Specific Enolase, Pancreastatin, Substance P, Pancreatic Polypeptide, and Atrial Naturetic Hormone (ANH).

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