Understanding small cell lung cancer and other neuroendocrine tumors

What is a neuroendocrine tumor?

A NET, also known as a neuroendocrine neoplasm or neuroendocrine carcinoma, is a rare tumor originating from neuroendocrine cells.

These cells are present in various organs of the body, including the:

• esophagus
• stomach
• lungs
• small and large bowel
• pancreas
• liver

Different types of NETs exist depending on where the cancer initially develops. For example, when a tumor starts growing in the lungs, doctors refer to it as a lung NET.

These tumors may not cause noticeable symptoms, which can delay diagnosis. This delay may allow NETs to spread to other parts of the body before doctors diagnose a person.

Types of lung neuroendocrine tumors

Approximately 20 in 100 of all NETs originate in the lungs.

According to the UK charity Cancer Research, there are four distinct types of lung NETs, including a specific type known as carcinoid tumors. The four lung NETs are:

• small cell lung cancer (SCLC)
• large cell neuroendocrine carcinoma (LCNEC)
• typical carcinoid
• atypical carcinoid

SCLC

SCLC is an aggressive type of cancer that grows quickly and rapidly spreads to other parts of the body. It accounts for about 15% of all lung cancers and has a strong association with smoking.

LCNEC

According to a 2022 article, LCNEC is a rare form of cancer that makes up about 3% of all lung cancers.

It is very aggressive and typically relates to heavy smoking. In most cases, the cancer spreads to other areas of the body before diagnosis.

Typical carcinoid

According to the American Cancer Society (ACS), typical carcinoid (TC) tumors are rare and less aggressive than SCLC and LCNEC.

The ACS states that around 90% of carcinoid tumors are TC and that they do not usually relate to smoking.

Atypical carcinoid

Atypical carcinoid (AC) tumors have a fast growth rate and a higher tendency to spread to other organs. AC tumors are less common than TC tumors and may be more common among individuals who smoke.

Risk factors

Risk factors vary for each type of NET. According to a 2022 article, SCLC and LCNEC associate with:

• smoking
• male sex
• older age

This article suggests that people with carcinoid tumors are typically younger, and the tumors have no association with smoking.

The ACS suggests further risk factors that may increase a person’s chance of having carcinoid tumors, including:

• being 45–55 years of age
• having multiple endocrine neoplasia type 1 (MEN1) syndrome
• having a family history of lung carcinoid tumors

It also suggests that smoking may be a risk factor for AC tumors.

Diagnosis

If a doctor suspects lung cancer, they may use various methods to determine if cancer is present, what type of cancer it is, and if the cancer has spread beyond the lungs.

According to the ACS, tests include:

• Chest X-ray: A chest X-ray helps doctors find any abnormalities in a person’s lungs.
• Computerized tomography (CT) scan: A CT scan uses specialized X-rays to capture detailed images of the body’s internal structures. Doctors may also use it for biopsy procedures.
• Positron emission tomography (PET) scan: A PET scan uses a sugar solution injection in a vein to highlight areas of potential cancer activity. Doctors may combine this with a CT scan.
• Magnetic resonance imaging (MRI) scan: An MRI scan uses radio waves and may help doctors learn if NETs have spread to other parts of the body.
• Biopsy: A lung biopsy involves the removal of a small portion of the lung tumor. Doctors may use this test to identify the type of lung cancer a person has.
• Bronchoscopy: In a bronchoscopy, doctors pass a thin tube through the mouth to visually inspect a person’s airways and collect tumor samples or fluid for analysis.

Treatment

Treatment approaches can vary for different types of lung NETs. They may also vary depending on the stage of the cancer and the overall health of the individual.

According to the ACS, doctors typically treat SCLC with a combination of chemotherapy and radiation therapy.

A 2022 article suggests that a combination of surgery and other treatments, such as chemotherapy and radiotherapy, results in the best outlook for people with LCNEC. The extent of surgery may depend on factors such as tumor size, location, and stage.

A combination of surgery and other therapies is also a common treatment for carcinoid tumors.

Outlook

Despite SCLC’s initial high responsiveness to chemotherapy, there is a high likelihood of cancer recurrence. Unfortunately, upon recurrence, the cancer may resist previously effective chemotherapy regimens.

While doctors can attempt alternative chemotherapy regimens, their effectiveness is typically lower. Moreover, the returning cancer is often extremely aggressive.

Other types of NETs may have a more promising outlook if doctors find and remove the cancer at an early stage. However, if the cancer spreads to other areas in the body, the outlook may be less favorable.

Summary

SCLC is an aggressive form of neuroendocrine cancer. NETs grow where neuroendocrine cells reside, which includes several areas in the digestive tract and lungs.

Other types of lung NETs include LCNEC and carcinoid tumors. Risk factors vary depending on the type of NET.

Treatment depends on the type of tumor, the location, and if the cancer has spread beyond the lungs. However, doctors will typically use a combination of treatments, such as chemotherapy, radiation therapy, and surgery.

The outlook for people with NETs may depend on an early diagnosis, a person’s overall health, and how well they respond to treatment.