Neuroendocrine Lung Cancer - A Group of Rare Lung Tumors

Introduction:

Neuroendocrine lung tumors are also called pulmonary neuroendocrine carcinomas. These types of carcinomas are usually rare and account for only two percent of all lung cancers. However, the lung is the second most common site to find neuroendocrine cells next to the gastrointestinal tract. Most of the neuroendocrine lung tumors are noncancerous (benign) and can be removed through surgery. But, in more than a quarter of people, the disease invades the neighboring tissue or spreads further to other areas (metastasize).

What Are the Types of Lung Carcinoid Tumors?

The following are the types of lung carcinoid tumors:

• Typical Carcinoids: These tumors constitute nine out of 10 lung carcinoids. They tend to grow slowly, and their spread beyond the lungs is rare.

• Atypical Carcinoids: These tumors are very rare and grow faster than typical lung carcinoids. There is a great probability that these tumors will spread beyond the lungs. Lung carcinoid tumors can also be classified based on their location. Central carcinoids are those that develop in the walls of the large airways of the lungs. Peripheral carcinoids develop close to the edges of the lungs in the smaller airways. The central and peripheral carcinoids are mostly typical carcinoids.

• Small Cell Lung Cancer (SCLC): Small cell lung cancer is the most common type of neuroendocrine tumor. It is considered to be aggressive and of high grade and is more likely to metastasize (spread) to other regions. SCLC not only causes cancer in the neuroendocrine cells but also in the cells of the submucosal lining of the airways.

• Large Cell Lung Carcinoma (LCC): LCC is a kind of non-small cell lung cancer (NSCLC). These, in rare cases, cause neuroendocrine lung cancer. LCC can be differentiated from SCLC by its size and is also regarded as high-grade due to its increased chances of metastasis.

Are Carcinoid Tumors of the Lung Common?

Lung carcinoid tumors are very rare and constitute just one to two percent of all lung cancers. About 2,000 to 4,500 new cases of lung carcinoid tumors are being diagnosed in the United States every year. Carcinoid tumors have an increased susceptibility to developing in other places of the body, like the digestive tract, more than in the lungs. Those who develop carcinoid tumors of the lungs are usually younger than those who develop other types of lung cancer.

What Are the Causes of Neuroendocrine Lung Cancer?

Neuroendocrine tumors have the potential to divide and grow abnormally and result in the development of cancerous tumors. The tumors that develop in the lungs are called pulmonary neuroendocrine tumors. Besides the lungs, these tumors can develop in the liver, colon, pancreas, ovaries, rectum, breast, thymus, thyroid gland, testes, prostate gland, adrenal glands, and pituitary gland. Though the exact causes of the manifestation of neuroendocrine tumors are not clear, there are several associated risk factors, which are as follows:

• Small Cell Lung Cancer (SCLC) and Large Cell Lung Carcinoma (LCC): The incidence of SCLC and LCC has been found to be strongly linked to cigarette smoking. About 95 % of individuals who suffer from this type of lung cancer are either current or former smokers. Occupational exposure to cancer-causing agents (carcinogens) and environmental pollutants are also some of the common risk factors. Men are more commonly affected by these tumors than women.

• Carcinoid Tumors: The manifestation of carcinoid tumors is rarely linked to environmental pollution, smoking, or occupational exposure. Children and young adults may be affected by this type of tumor. This tumor has a female predilection, and more whites are affected. It is believed that family history and genetics play a role in the manifestation of carcinoid tumors. Carcinoid tumors are linked with a number of genetic syndromes like multiple endocrine neoplasia type 1 (MEN1- a hereditary condition linked with tumors of the endocrine glands).

What Are the Symptoms of Neuroendocrine Lung Cancer?

Neuroendocrine lung tumors may not cause any noticeable symptoms until they grow larger or spread. When this happens, the symptoms may mimic that of asthma. The symptoms of neuroendocrine lung cancer are as follows:

• A cough that does not resolve and which varies in intensity throughout the day.

• Fatigue.

• Coughing up small quantities of blood.

• Pain in the chest or shoulders.

• Frequent chest infections like pneumonia, or an infection that is unresponsive to treatment.

• Shortness of breath.

How Can Neuroendocrine Lung Tumors Be Diagnosed?

Not all diagnostic tests are employed in all individuals to diagnose neuroendocrine lung tumors (NET). The following factors are considered while choosing a diagnostic test:

• The type of tumor that is suspected.

• The age and overall health of the individual.

• The signs and symptoms.

• The results of previous medical tests.

A majority of lung NETs are diagnosed unexpectedly when individuals get medical procedures or imaging tests done for other reasons. If NET is suspected, then the physician will do a complete physical examination and enquire about the complete family and medical history of the individual. The following are a few diagnostic tests that are done to diagnose lung NET:

• Biopsy: For biopsy, a small amount of tissue is removed from the individual to be examined under a microscope. A biopsy is considered to be the only method of arriving at a definitive diagnosis though other tests may suggest the possibility of a cancer.

• Bronchoscopy: It is a type of endoscopy in which a thin, flexible, lighted tube called a bronchoscope is used to visualize the inside of the airways and lungs. In case an abnormality is detected, a biopsy will be performed.

• Endobronchial Ultrasound: In this procedure, sound waves are utilized to produce an image of the internal organs. Endobronchial ultrasound can display enlarged lymph nodes, which enables the physician to detect a tumor or identify the stage of the disease.

• Nuclear Medicine Imaging: In this procedure, a small amount of a radioactive drug known as the tracer is injected into the patient’s vein. The body is then scanned to detect where the radioactive drug has accumulated in the body.

• Other Tests - X-ray, CT (computed tomography), MRI (magnetic resonance imaging), blood and urine tests.

How Are Neuroendocrine Lung Cancers Treated?

Neuroendocrine lung cancers are treated depending on their size and location, symptoms, type of tumor, extent of spread (if any), how fast it is growing, and the individual’s overall health. Some of the common treatment modalities are as follows:

• Surgery: Surgery or resection refers to the removal of the tumor along with some of the surrounding healthy tissue. Complete removal of the tumor is considered the standard treatment. Some of the common surgical options include sleeve resection, sub-lobar resection (wedge resection or segmentectomy), lobectomy (removal of a lung lobe), liver resection, lymph node dissection, and pneumonectomy (removal of an entire lung).

• Chemotherapy: In chemotherapy, several types of drugs like Carboplatin, Temozolomide, Cisplatin, and so on are used to kill cancer cells.

• Somatostatin Analogs: Somatostatin analogs inhibit the body from manufacturing too many hormones. This may retard the growth of the tumor when cancer cells have migrated (metastasized) to other parts of the body.

• Targeted Therapy: In targeted therapy, drugs are utilized to target certain proteins or genes to kill cancer cells.

• Radiation Therapy: Radiation therapy utilizes high-energy X-rays or other particles to destroy cancer cells. The preferred radiation treatment for neuroendocrine lung cancer is external-beam radiation therapy in which radiation is emanated from a machine outside the body.

Conclusion

A neuroendocrine tumor (NET) originates in the specialized cells of the body’s neuroendocrine system. These cells have characteristics of both nerve cells and hormone-producing endocrine cells. NETs most commonly develop in the lungs or the gastrointestinal tract. However, they can develop in the pancreas or other sites throughout the body. Surgery is the most preferred choice for treating neuroendocrine lung cancers. These are very rare tumors, and the long-term prognosis of neuroendocrine tumors is measured by the five-year survival rate, which is generally good when compared to other types of lung cancers.