There are a few types of tumors that can neither be classified as benign (noncancerous) or malignant (cancerous). Their clinical behavior falls between the two classifications of benign and malignant, and they have sometimes been called "midway" tumors. They were so named in an attempt to designate these tumors as midway between cancers and benign tumors. Among these rare tumors are carcinoid tumors.
Carcinoid tumors have also been called "cancers in slow motion." Even though they have the potential for being malignant, they mostly tend to grow so slowly that people with carcinoid tumors usually live for many years (sometimes for a normal lifetime).
Carcinoid lung tumors are an uncommon group of lung tumors, developing from neuroendocrine cells. The neuroendocrine cells are in some respect like nerve cells and in other ways like cells of endocrine (hormone-producing) glands. These cells are scattered throughout the body and can be found in different organs, for instance, the lungs, stomach, and intestines. These neuroendocrine cells can form growths (tumors) in many different organs, but usually occur in other endocrine glands such as the adrenal or thyroid glands, or the intestinal tract.
The uncontrolled growth of neuroendocrine cells leads to the development of carcinoid tumors. Most carcinoid tumors originate in the small intestine, but carcinoid lung tumors represent about 10% of all carcinoid tumors. Carcinoid lung tumors comprise 1%-6% of all lung tumors.
There are two types of carcinoid lung tumors: typical and atypical.
1. Typical carcinoid lung tumors are about nine times more common than atypical carcinoid lung tumors. These tumors characteristically grow slowly and only rarely metastasize (spread) beyond the lungs.
2. Atypical carcinoid lung tumors are more aggressive than typical carcinoid lung tumors and are somewhat more likely to metastasize to other organs. They comprise about 10% of all carcinoid lung tumors.
Some carcinoid tumors produce hormone-like substances that can cause a number of endocrine syndromes. The term carcinoid syndrome has been used to refer to the collection of symptoms produced when a carcinoid tumor secretes hormone-like substances. These syndromes tend to reflect the excessive response of the body to the hormone-like substances produced. However, carcinoid syndrome occurs in only about 2% of people with carcinoid lung tumors.
About 25% of lung carcinoid tumors are located within the airways and are referred to as bronchial carcinoids. These are not related to smoking or other environmental causes. While anyone can develop a carcinoid tumor of the lung, they may be slightly more common in African-American males.
CAUSES OF CARCINOID TUMOR
Unlike most lung cancers, no external environmental toxin (for example, tobacco smoke, air pollution, asbestos, radon) has been identified as a causative agent for the development of carcinoid lung tumors.
SIGNS AND SYMPTOMS
About 25% of persons with carcinoid lung tumors are asymptomatic (have no symptoms) at the time of discovery. Most of the time, carcinoid lung tumors are found on a routine chest X-ray done for unrelated medical problems (referred to as an incidental finding).
The severity and range of symptoms depend on the size of the tumor and whether or not it produces hormones.
Persons with carcinoid lung tumors may complain of the following symptoms:
• Cough that does not go away
• Coughing up blood (50%)
• Chest pain
• Difficulty in breathing
• Wheezing
• Fever (due to infection in the lung)
Sometimes the health care practitioner considers the possibility of a tumor only after treatment with antibiotics fails to cure a lung infection.
Although uncommon, symptoms of various endocrine syndromes (carcinoid syndrome) can be the initial indicator of carcinoid lung tumors.
The symptoms of carcinoid syndrome include the following:
• Facial flushing (redness and a warm feeling that may last hours to days)
• Sweating
• Diarrhea
• Fast heartbeat
• Weight gain
• Increased facial and body hair
• Increased skin pigmentation
In persons with malignancy (rare), the presence of metastatic disease can produce the following:
• Weight loss
• Weakness
• General feeling of ill health
TREATMENT
Medical Treatment
There is no medical therapy for the treatment of carcinoid lung tumor.
Surgery is the primary treatment for carcinoid lung tumors.
• Chemotherapy (using medications to kill cancer cells) and radiation therapy (using high-dose X-rays or other high-energy rays to kill cancer cells) have been used in the treatment of carcinoid lung tumors that have spread; however, no success has been achieved.
• A response rate of 30%-35% has been reported using a combination of the drugs 5-fluorouracil (Adrucil) and streptozotocin.
• If the patient is having symptoms associated with carcinoid syndrome (for example, flushing, diarrhea) he or she may be given a drug called octreotide (Sandostatin). Octreotide is not a cure; it is used only when the disease has spread and the patient has symptoms associated with carcinoid syndrome.
• Another drug (MIBG) is taken up by carcinoid cells and damages them. Researchers are studying MIBG to see if it is effective in the treatment of carcinoid lung tumors.
• In some malignant cases, the tumor can spread to the liver. If this is a solitary mass, it may be treated with chemotherapy directed at the hepatic artery feeding the location of the tumor.
PREVENTION
Unlike most lung tumors, carcinoid lung tumors have not been associated with smoking, air pollution, or other chemical exposures. Therefore, there are no known ways to prevent carcinoid lung tumors.
