A carcinoid tumourlet is a small, non-cancerous growth found in the lungs. It is made up of special cells called neuroendocrine cells. Neuroendocrine cells are normally found throughout the lungs, especially in the airways. When these cells group together and grow slightly more than normal, they can form tiny structures called tumourlets. To be called a carcinoid tumourlet, the group of cells must be smaller than 5 millimeters (about the size of a sesame seed) and show no abnormal signs such as mitotic activity (cell division) or necrosis (cell death).
Are carcinoid tumourlets cancer?
No. Carcinoid tumourlets are not considered cancer. They are small, harmless groups of neuroendocrine cells that grow more than normal but do not behave like cancer. They do not spread to other parts of the body.
Carcinoid tumourlets are closely related to larger growths known as carcinoid tumours, which can be cancerous. However, carcinoid tumourlets are smaller and do not have the features that would make them cancer.
What causes carcinoid tumourlets?
The exact reason why carcinoid tumourlets develop is not fully known. They are more common in people who have lung conditions involving ongoing inflammation or scarring. Conditions such as bronchiectasis (permanent enlargement of the airways) or chronic bronchitis have been linked to an increased chance of developing carcinoid tumourlets. They are also often found incidentally, meaning they are discovered by accident when lung tissue is removed for other reasons, such as surgery for lung cancer or lung biopsy.
What are the symptoms of carcinoid tumourlets?
Most people with carcinoid tumourlets do not experience any symptoms because these growths are very small. They are usually discovered during tests or surgeries done for other lung conditions. Occasionally, multiple tumourlets may appear in people with certain chronic lung diseases, but they still typically do not cause specific symptoms.
How is the diagnosis of a carcinoid tumourlet made?
The diagnosis of carcinoid tumourlet can only be made by examining lung tissue under a microscope. This usually happens after lung tissue is removed during surgery for another condition. Pathologists carefully examine the tissue and identify small groups of neuroendocrine cells measuring less than 5 millimeters without abnormal features like mitotic activity (cell division) or necrosis (cell death). When these features are seen, the diagnosis of a carcinoid tumourlet is made.
What do carcinoid tumourlets look like under the microscope?
Under the microscope, carcinoid tumourlets look like small, round groups of uniform cells. Pathologists describe these cells as having a “salt and pepper” pattern because their nuclei (the part of the cell containing genetic material) contain small dark dots on a lighter background. This pattern is common for neuroendocrine cells. Importantly, there should be very few mitotic figures (dividing cells) and no signs of necrosis (cell death). Tumourlets blend into the surrounding lung tissue and do not invade or damage nearby structures.
Is treatment required for carcinoid tumourlets?
No. Because carcinoid tumourlets are harmless and not cancer, no additional treatment is needed once they are found. They do not spread or grow aggressively, so doctors typically do not recommend further monitoring or therapy specifically for tumourlets.
If carcinoid tumourlets are found, your doctor may discuss the findings to reassure you and explain that no additional treatment or follow-up is required.
Questions for your doctor
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Do I need any follow-up testing or imaging because of this diagnosis?
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Are carcinoid tumourlets related to my other lung conditions?
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Should I watch for any symptoms or changes related to this diagnosis in the future?
