About 30% of NETs occur in the lungs. A lung NET may not cause symptoms in its early stages. Lung NETs are sometimes discovered when patients are screened for unrelated diseases.
Lung NETs may be further described based on where they occur in the lungs.
Central: forms in the walls of large airways near the center of the lung
Peripheral: develops in the narrow airways toward the edge of the lung
In addition to the lungs, a lung NET can form in the bronchial system (the air
passages that lead to the lungs).
Depending on how fast a lung NET is growing, it may be further classified as:
Typical carcinoid (TC): may grow slowly and are often centrally located.
Atypical carcinoid (AC): may grow a little faster and are more likely to spread beyond the lungs. They are often peripherally located.
The most aggressive lung NET is small cell lung carcinoma, which is almost always related to smoking.
Lung NETs can cause symptoms when they block an airway, such as:
A functional lung NET, which releases hormones into the blood, may also cause a few other symptoms such as Cushing’s syndrome.
NETs can occur throughout the body, but most commonly form in the GI tract, pancreas, lungs and adrenal glands.