What Is Lung Carcinoid?

Lung carcinoid tumors form when neuroendocrine cells turn cancerous. These cells produce hormone-like substances (neuropeptides) that regulate lung functions, such as gas exchange and monitoring oxygen-carbon dioxide levels. A lung carcinoid is a malignant (cancerous) tumor with the following properties:

• Slow-growing
• Neuropeptide-secreting
• Molecular and genetic profile

Compared to other lung cancer subtypes, it is uncommon, accounting for only 2% of all lung cancer cases.

Lung carcinoid belongs to a group of lung cancer subtypes called lung neuroendocrine tumors (NETs).

Understanding more about lung carcinoid and its slow growth rate can help detect and treat it early. This article will delve more into its risks and testing so that proactive measures can be taken to protect your health.

Sometimes, lung carcinoid tumors are indicated based on where they form in the lung:

• Central carcinoid – forms in the lining of the main airway (bronchi). It is also known as bronchial carcinoid.
• Peripheral carcinoid – forms in the lining of smaller airways (bronchioles) that branch away from bronchi towards the peripheral area of the lungs.

Lung carcinoids can also be classified by their aggressiveness:

• Typical carcinoid – the least aggressive type of lung NETs. It is generally slow-growing and rarely spread outside the lung. Often detected as a localized tumor, thus has a better outlook.
• Atypical carcinoid – behaves slightly more aggressively than typical carcinoid. In other words, it grows faster than typical carcinoid and tends to spread beyond the lung.

Read more: Key Statistics for Lung Carcinoid Tumor

The association between lung carcinoids and other lung cancer-related risk factors remains unclear, although some studies suggest:

• Lung carcinoids are more common among females than males
• Lung carcinoids occur more often in Whites than in other ethnic
• The average age at diagnosis for typical carcinoid tumor is 45 years and 55 years for atypical carcinoid tumor. This is slightly younger than the average diagnosis age for other subtypes of lung cancer
• Although rare, some lung carcinoid cases can be hereditary with mutations in MEN1 gene

The detection of lung carcinoid tumor is typically incidental and often occurs when imaging studies are conducted for other reasons. . The diagnosis of lung carcinoid is confirmed by microscopic evaluation of biopsy specimen acquired via:

• Bronchoscopic biopsy – for central carcinoid
• Transthoracic needle biopsy – for peripheral carcinoid

Staging of lung carcinoid uses the same Tumor, Node, Metastasis (TNM) classification as other subtypes of lung cancer. Most of the typical carcinoid cases are found at Stage 1 at the time of diagnosis. More than half of atypical cases (more aggressive carcinoid) are diagnosed at stage 2 or 3.

The pathology report of a lung carcinoid tumor may include:

• Biopsy site – from the inside of bronchi lining or from the areas of lung outer edge
• Shapes and size of individual tumor cells – terms used include polygonal, granular, eosinophilic, round nuclei, spindle-shaped, organoid, trabecular, rosette formation, nested
• Mitotic activity - number of cells that are dividing; is a prognostic factor for overall survival and predicts response to treatment. Atypical carcinoid has a higher proportion of dividing cells (higher mitotic count)
• Necrosis - absence of cell death is one of the features that gives “typical” carcinoid its classification; presence of cell death in atypical carcinoid suggests a more aggressive behavior .
• Marker staining - Pathologists will sometimes run immunohistochemical staining on biopsy or surgical samples to make a definitive diagnosis.

There is no guideline or recommendation for biochemical workup (blood test) or marker staining for a lung cancer subtype that is as rare as lung carcinoid. However, under specific circumstances, doctors may order lab tests:

• If a patient presents carcinoid syndrome – Neuroendocrine or hormonal markers may be present in the urine or blood of individuals with clinical symptoms of carcinoid syndrome. Carcinoid syndrome is caused by an excess level of serotonin hormone produced by a carcinoid tumor. Patients with carcinoid syndrome may have higher levels of 5-hydroxyindoleacetic acid (5-HIAA), a breakdown component of serotonin, in their urine. However, a 5-HIAA assay may give false positive results for various reasons like other medical conditions and consumption of certain foods or medicines.
• A blood test may detect other carcinoid syndrome-related hormonal markers like cortisol, chromogranin A (CgA) and neuron-specific enolase (NSE). But again, it is likely that the tests are not useful in diagnosing lung carcinoid. Unlike other carcinoid tumors, such as gastrointestinal carcinoids, lung carcinoid tumors secrete a much lesser amount of hormonal markers mentioned above into the blood. Consequently, the detection may not be sensitive enough to give accurate results.
• To help diagnose difficult cases, doctors may order immunohistochemical staining of markers like CgA, synaptophysin, or CD56 on biopsied specimens. These markers are used to differentiate lung tumors with neuroendocrine properties (i.e., lung carcinoid) from other types of lung tumors.

Surgical removal is often the primary treatment for lung carcinoids, especially if the tumor is localized and has not spread to nearby tissues or lymph nodes. In some cases, it is necessary to remove nearby lymph nodes or additional tissue that has turned cancerous. The goal is to ensure complete removal of the tumor and any cancer cells in surrounding tissues. Depending on the tumor’s location and size, lung resection procedures, like lobectomy, pneumonectomy or segmentectomy, may be employed. Radiation therapy may be considered in cases where surgery is not possible or to shrink the tumor before surgery.

For patients with advanced disease (i.e. those in whom the disease involves multiple parts of the lung or which has spread beyond the chest to other organs), treatment options include somatostatin analogs and chemotherapy. Somatostatin analogs are a class of drugs that control symptoms by stopping hormone release by the tumor. It may also help to control tumor growth in some lung carcinoid cases.

Given the rarity of lung carcinoids, the development of treatments for lung carcinoids has been relatively limited. Participation in clinical trials may be an option for some patients if standard treatments have been ineffective. These tumors are relatively uncommon, making them harder to detect early for effective treatment. Early testing and diagnosis can make a difference. Therefore, individuals should take a proactive approach to catch any potential issues early on.