Carcinoid tumors, lung

Encyclopedia of Cancer, 20050229 by Maureen Haggerty

Definition

Lung carcinoid tumors are rare malignant growths that develop from cells that help regulate the flow of air and blood through the lungs. These growths are also known as neuroendocrine lung tumors, pulmonary carcinoids, and lung carcinoids.

Description

These cancers account for 1% to 3% of all lung tumors. Most lung carcinoids measure between slightly less than 1/4" (0.63 cm) and slightly more than 3/4" (1.9 cm). These tumors usually develop in the right lung.

Doctors classify lung carcinoids according to what tumor cells look like under a microscope, and where in the lung the tumor is located. Typical lung carcinoids occur about nine times as often as atypical tumors. They grow slowly and rarely spread beyond the lungs. Atypical lung carcinoids grow somewhat faster than typical tumors and are more likely to spread to other organs. In their most invasive form, atypical lung carcinoids look and behave like small-cell lung cancers.

About 80% of lung carcinoids are central carcinoids. Located in the walls of the large airways in the center of the lungs, where the neuroendocrine cells that form them are most concentrated, these tumors are almost always typical tumors. Carcinoids that develop in the narrower airways, close to the edges of the lungs, are called peripheral carcinoids. Most are typical tumors.

Demographics

Lung carcinoids usually develop between the ages of 45 and 55. These tumors are equally common in men and women and rarely affect children.

Causes and symptoms

Lung carcinoids are not caused by smoking or by exposure to chemicals at work or in the environment. Doctors believe that central carcinoids develop from glands beneath the surface of the large air passages. Lung biopsies performed to diagnose or treat other conditions sometimes reveal microscopic clusters of neuroendocrine cells. These carcinoid tumorlets look like tiny peripheral carcinoids. They are most common when disease has caused scar tissue to form in the lungs, and may grow to be carcinoid tumors.

Patients who have peripheral or small central carcinoids don't usually show symptoms, but some patients who have central carcinoids cough, wheeze, or cough up blood (hemoptysis).

A large carcinoid that blocks part or all of an airway can cause post-obstructive pneumonia. Doctors may not consider the possibility of a carcinoid until antibiotics fail to cure this lung infection.

About 10% to 20% of lung carcinoids produce hormone-like substances that release into the bloodstream. These substances can cause symptoms such as Cushing's syndrome, acromegaly, or hypercalcemia. They may also cause carcinoid syndrome, which is a constellation of symptoms including facial flushing, abdominal cramps, diarrhea, and breathlessness, among others.

Diagnosis

A thorough physical examination will detect symptoms of syndrome health problems associated with these tumors. If a patient has one or more symptoms that suggest the presence of a lung carcinoid, the doctor will inquire about:

chest pain

cough

blood-tinged sputum

asthma

wheezing

pneumonia not cured by antibiotics

recent weight gain

facial flushing

diarrhea

The doctor will use one or more methods to determine whether the patient has a lung tumor. Lung carcinoids that do not cause symptoms usually show up on chest x rays taken during a routine physical or as a result of other health problems.

Chest x rays cannot detect tumors that are very small or hidden by other organs in the chest. A doctor who suspects a lung carcinoid may order additional imaging studies in order to make a more detailed search.

About 75% of lung carcinoids can be seen through a long, lighted tube called a bronchoscope. Doctors also use CT scans, octreoscans, or MIBG (metaiodobenzyl-guanidine) scans to locate lung carcinoids and determine how far they have spread. CT scans provide a detailed view of the lungs. Octreoscans and MIBG scans trace the path of radioactive substances that are attracted to lung carcinoids.

Also called indium-111-labeled DTPA-octreotide scintigraphy, octreoscan involves injecting a small amount of a radioactive hormone-like substance into the patient's vein. Carcinoid tumors attract this substance, and a special camera locates tumors by pinpointing the area where the radioactive material accumulates.

Doctors perform MIBG scans by attaching radioactive iodine to a chemical absorbed by carcinoid tumors. This compound is injected into the patient's bloodstream, drawn to carcinoid tumor cells, and tracked by a special scanner.

Although diagnostic procedures can indicate that a patient might have a lung carcinoid, biopsy is the only way to confirm the diagnosis. Doctors use several different techniques to remove samples of these tumors.

Bronchoscopic biopsy

To obtain a sample of a tumor in one of the large airways, the doctor uses a bronchoscope to examine the lining of these organs. When a tumor is located, the doctor manipulates pincers or tongs (biopsy forceps) through the bronchoscope to remove a small sample of tissue. The patient leaves the hospital a few hours after undergoing this outpatient procedure. If serious bleeding occurs, the doctor narrows or seals the blood vessels by injecting drugs or aiming a laser beam.