Neuroendocrine cells help heal the thin layer of tissue — known as the epithelium — that lines internal organs and other surfaces inside the body after injury, including injury from infection. Occasionally, however, neuroendocrine cells become overactive and, eventually, may become cancerous.
A small percentage of all lung cancers are neuroendocrine tumors. Because neuroendocrine cells are found throughout the body, neuroendocrine tumors can arise in a variety of organs, not just in the lungs. In fact, the vast majority of the time, they occur in the gastrointestinal system. For more information about neuroendocrine tumors in the gastrointestinal system, please visit the Gastrointestinal Neuroendocrine Tumors section of our website.
Doctors may diagnose and treat neuroendocrine tumors according to the types of cells involved, how the tumor cells look under the microscope, and where they are in the body.
Types of Pulmonary Neuroendocrine Tumors
There are several types of neuroendocrine tumors that can arise in the lungs.
Up to 25 percent of all carcinoid tumors are found in the lungs. The majority of these tumors develop in the major bronchi (large tubes that lead air from the windpipe into the lungs). There is no direct evidence that smoking causes pulmonary carcinoid tumors, yet studies suggest that a higher percentage of patients with atypical pulmonary carcinoid tumors smoke.
Pulmonary carcinoid tumors are further classified as follows:
- Typical Carcinoid Tumors: The majority of all pulmonary carcinoid tumors are typical (low-grade), which means that they are slow-growing cancers.
- Atypical Carcinoid Tumors: Atypical (intermediate-grade) pulmonary carcinoid tumors are more rare. These tumors grow more rapidly than typical carcinoid tumors, but are much less aggressive than non-carcinoid tumors in the lungs, such as adenocarcinoma of the lungs.
This fast-growing type of cancer represents a small percentage of all lung cancers. Large cell neuroendocrine carcinoma of the lungs is four times more common in men than in women. Smoking is a significant risk factor for developing this type of lung cancer.
Small cell lung carcinoma accounts for about 10 to 13 percent of all lung cancers. Like large cell neuroendocrine carcinoma, this type of cancer also occasionally arises in the gastrointestinal tract. Smoking is the single biggest risk factor for developing small cell lung carcinoma. Additional risk factors include exposure to radon and asbestos. Small cell lung cancer also can occur in people with certain electrolyte and neurologic disorders.
The symptoms of these tumors may be similar to each other.
Because they frequently develop in the bronchial tubes, pulmonary carcinoid tumors can cause symptoms such as:
- coughing up blood
- recurrent pneumonia
Some people also may develop pain in the chest wall. However, up to one-third of patients with carcinoid tumors in the lungs have no symptoms.
Pulmonary carcinoid tumors can cause a variety of symptoms known as carcinoid syndrome. These symptoms, including diarrhea, flushing, and wheezing, may occur when the tumors produce excess serotonin, a hormone found in blood platelets, the digestive tract, and the brain. Carcinoid syndrome is more common in patients with gastrointestinal carcinoid tumors.
In rare cases, carcinoid lung tumors may produce too much ACTH, a substance that causes the adrenal glands to make too much cortisol and other hormones. This can lead to weight gain, weakness, diabetes, increased body and facial hair, and thin or darkened skin (Cushing’s syndrome). Less common symptoms of lung carcinoid tumors may include sudden growth of the hands and feet (acromegaly) and increased blood calcium (hypercalcemia).
Large cell neuroendocrine carcinoma of the lungs and small cell lung carcinoma can cause symptoms such as:
- recurrent pneumonia
- chest wall pain
However, many people with these types of tumors experience no symptoms.