An Overview of Carcinoid Tumors of the Lung

Symptoms, causes, diagnosis, and treatment

Carcinoid lung tumors account for 2–5 percent of less of lung cancers and differ in many ways from the better-known lung cancers. Typical and atypical carcinoids can occur at any age, and are the most common type of lung tumor found in children. Symptoms may include a cough, coughing up blood, wheezing, or recurrent chest infections, and often develop early, as many of these tumors are found near the large airways.

Carcinoids may also have symptoms unrelated to the lungs due to the hormone-like substances they can secrete. They are often found on a chest CT scan, with a lung biopsy done to confirm the diagnosis. For early-stage tumors, surgery is the treatment of choice. For advanced cancers, the biological therapy everolimus is the only approved drug, but many other treatments are being evaluated in clinical trials.

Carcinoid tumors have little association with smoking unlike other lung cancers, and, with the exception of some genetic syndromes, no clear risk factors have been identified. They are more common in women than men, and in white people than black people.

The incidence of carcinoid tumors of the lung is increasing. It's also thought that some of these tumors are misdiagnosed as being lung adenocarcinoma.

Overall, carcinoids are a very heterogeneous group of cancers, and one tumor may behave and respond to treatment much different than another.

Types

Carcinoid tumors are a form of neuroendocrine tumor, tumors that begin in the neuroendocrine cells that line many organs in the body such as the airways. These cells are responsible for aiding in the growth and repair of lung cells, as well as regulating air and blood flow in the lungs (by sensing oxygen and carbon dioxide levels).

Carcinoid tumors of the lung are divided into two primary types:

  • Typical Carcinoid Tumors: Typical carcinoids or low-grade carcinoids are made up of cells that appear very much like normal cells; that is, they are well-differentiated. Accounting for roughly 90 percent of lung carcinoids, these tumors tend to grow slowly.
  • Atypical Carcinoid Tumors: Atypical or intermediate grade carcinoids are also considered to be "well-differentiated" but the cells are more abnormal-appearing than those found in typical carcinoids. These tumors tend to grow (and spread) more rapidly than typical carcinoids but are usually less aggressive than the more common types of lung cancer.

Symptoms

Carcinoid tumors of the lung, especially typical carcinoids, tend to grow centrally near the large airways and cause symptoms early on. Common symptoms are often due to the tumor obstructing the airway, and include:

Atypical carcinoids may grow centrally or peripherally in the lungs. With peripheral lung tumors, the first symptom is often shortness of breath. Early on, this may occur only with exercise.

Symptoms of Advanced Disease

Less commonly, carcinoids may present with symptoms of advanced cancer such as loss of appetite and weight loss.

Unique Symptoms

Some carcinoid tumors secrete hormones or hormone-like substances that give rise to a number of symptoms not usually associated with lung cancers. These can include:

  • Carcinoid Syndrome: Some carcinoids release substances such as serotonin that cause facial flushing (that can be dramatic), wheezing, and watery diarrhea.
  • Cushing's Syndrome: Some carcinoids secrete the hormone ACTH (adrenocorticotropic hormone) that causes the symptoms of Cushing's syndrome. Symptoms include weight gain, a moon-like appearance of the face, accumulation of fat between the shoulders ("buffalo hump"), high blood pressure, and muscle weakness. While not common overall, it occurs frequently in carcinoid tumors associated with MEN1 syndrome.
  • Hypercalcemia: Some carcinoids secrete substances the lead to an increased calcium level in the blood. This can lead to weakness, cramping, nausea, and lethargy. When severe, loss of consciousness may occur.
  • Acromegaly: Carcinoids that secrete growth hormone may result in enlargement of the hands and feet as well as facial changes (acromegaly in adults), or rapid growth (in children).

Causes and Risk Factors

Few risk factors have been identified in association with Carcinoid syndrome.

Smoking

Unlike many types of lung cancers, carcinoid tumors do not have a strong association with smoking.

Genetics

Having a family history of carcinoid tumors increases risk, but most people do not have a family history. There are some genetic syndromes that are associated with an increased risk, including multiple endocrine neoplasia 1 (MEN1).

Diagnosis

The diagnosis of carcinoid tumors is sometimes challenging early on. For example, carcinoid tumors that secrete ACTH may have the gradual appearance of symptoms that are almost identical to Cushing's syndrome before any lung symptoms occur.

Imaging

A number of imaging tests may be done, though it's important to note that carcinoids can sometimes mimic benign tumors.

  • Chest X-Ray: Carcinoid tumors are often missed on plain chest X-rays, but may be suspected when a chest X-ray is done.
  • Chest CT: A chest CT can often detect carcinoid tumors.
  • Somatostatin Receptor Scintigraphy: Scintigraphy is a test that uses a radioactive particle attached to octreotide that is injected into the body. Octreotide binds to carcinoid tumors, and gamma rays from the radioactive particle are then detected to find the tumor.

Procedures

  • Bronchoscopy: In a bronchoscopy, a flexible tube is inserted through the mouth and threaded down into the large airways (bronchi) of the lungs. Since many carcinoids are located near the airways, these tumors can often be seen. An endobronchial ultrasound (using an ultrasound tool to view the tissues beneath the airways) may be helpful, and a biopsy may be done via this procedure as well.
  • Lung Biopsy: Even if a carcinoid is suspected, a biopsy is needed to confirm the diagnosis and distinguish between typical and atypical carcinoids. A needle biopsy may be done by inserting a fine needle through the chest wall and taking a sample of the tumor. In an open lung biopsy, a tumor is biopsied directly during surgery.

Blood Tests

For carcinoid tumors that secrete hormones, tests for the hormones that are sometimes secreted may be done. Another test, called the Ki67 proliferation index can sometimes help distinguish carcinoids from other types of lung cancer, as well as predict those people with carcinoids who may respond to chemotherapy (most do not).

Staging

Unlike the more common lung cancers, staging tests are not always needed with carcinoid tumors since they grow slowly and are unlikely to spread. Since most carcinoid tumors are slow-growing (have low metabolic activity) they are unlikely to show up as malignant on a PET scan. A CT scan (or MRI) may be done to look for spread to the liver.

Treatment

Since carcinoid tumors can vary significantly, the treatment options can also vary. For early-stage disease, the treatment of choice is surgery. For advanced carcinoid tumors, there is currently only one drug approved, but several others are being evaluated.

Surgery

Depending on the size and location of the carcinoid, one of the types of lung cancer surgery is usually recommended. For small tumors, a lobectomy or even a wedge resection may be considered, and for larger tumors (or those in certain locations) removal of an entire lung (pneumonectomy) may be recommended.

Biological Therapy

The biological therapy drug Afinitor (everolimus) is recommended for advanced typical and atypical carcinoids that do not secrete hormones or hormone-like substances. Approved in 2016, it can improve survival and is quite well tolerated. It is taken as a daily pill rather than as an intravenous therapy. Afinitor is classified as an mTor inhibitor and works by interrupting a signaling pathway that is needed for cancer to grow.

Somatostatin Analogues

The drugs Sandostatin (octreotide), Somatuline (lanreotide), and Signifor (pasireotide) are somatostatin analogs and are used for people with low-grade carcinoid tumors that secrete hormone-like substances. They can be used to control the growth of the tumor (and reduce symptoms) but are not a curative treatment.

Chemotherapy

In general, most carcinoids do not respond to chemotherapy agents, although these drugs may be tried in some cases.

Radiation Therapy

Radiation is used infrequently with carcinoid tumors, although radioactive particles combined with drugs are being studied. In some cases, such as if a tumor is early but cannot be removed surgically for some reason, specialized radiation treatments such as Cyberknife (stereotactic body radiotherapy) may be used as an alternative to surgery.

Clinical Trials

There are a number of options being evaluated for carcinoids in clinical trials that are promising. Examples include radioactive particles combined with octreotide.

Prognosis

When carcinoid tumors can be removed surgically, the prognosis is relatively good. With advanced disease, the approval of Afinitor has increased survival, and other treatments are being studied actively. Carcinoid tumors associated with the genetic syndrome MEN1 tend to be more aggressive with lower survival rates.

Coping and Support

Since carcinoid tumors are relatively uncommon, it's important to find a physician who is familiar with the disease. Some of the larger cancer centers, such as the National Cancer Institute-designated centers, are often more likely to have oncologists on staff who have treated a number of other people with these cancers. These larger centers are also more likely to offer clinical trials looking at the newer treatments for advanced carcinoids.

Many communities do not have a local support group for people with carcinoid tumors, but online support communities allow you to connect with others around the country facing similar challenges. The Carcinoid Cancer Foundation is a non-profit organization committed to supporting people with carcinoid tumors alone. In addition to organizations, there are Facebook groups, and the hashtag #Carcinoid can help you find others on social media sites such as Twitter.

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Article Sources
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  • Melosky, B. Advanced Typical and Atypical Carcinoid Tumors of the Lung: Management Recommendations. Current Oncology. 2018. 25:86. DOI: 10.3747/co.25.3808.