Most lung cancers are classified as either non-small cell lung cancer (NSCLC) or small-cell lung cancer (SCLC). SCLC is less common but tends to be more aggressive. It’s subdivided into two main types: pure SCLC and combined SCLC.

Small-cell lung cancer (SCLC) makes up about 15% of the nearly 240,000 lung cancer cases diagnosed in the United States each year. Smoking of tobacco products is by far the top risk factor.

The names “SCLC” and “NSCLC” come from the way the cancer cells look under a microscope. SCLC cells look small and round, and NSCLC cells look larger than usual.

The classification system for SCLC has changed over the years, but the most recent guidelines from the World Health Organization (WHO) classify it into two categories: “pure SCLC” if the cancer’s features are purely SCLC and “combined SCLC” if it also has features of NSCLC.

In this article, we take a deeper look at these two types of SCLC, including their symptoms, treatment options, and outlook.

SCLC is also called oat cell carcinoma because of the microscopic appearance of its cells. The most common form of SCLC is also called pure SCLC if it doesn’t have any features of NSCLC.

Pure SCLC makes up about 80% of cases of SCLC, although estimates vary across studies.

SCLC is classified as a neuroendocrine tumor, meaning that it starts in neuroendocrine cells or cells that can produce hormones in response to neurological signals.

Combined SCLC occurs when the cancer cells also have features of NSCLC. It makes up roughly 20% of cases of SCLC.

People with combined SCLC most commonly have features of a type of NSCLC called large cell carcinoma.

Combined SCLC may less commonly be combined with squamous cell carcinoma and adenocarcinoma.

At least 10% of the cancerous cells in a lung cancer tumor need to have a large cell carcinoma, or LCNEC, component for doctors to diagnose combined SCLC. There are no percentage requirements if SCLC is mixed with other NSCLC subtypes.

The symptoms, response to chemotherapy, and survival rates of pure SCLC and combined SCLC are similar.

The main symptoms are:

SCLC is also the disease most commonly associated with paraneoplastic syndromes, which occur when cancerous neuroendocrine cells start producing excess hormones that can lead to many groups of symptoms. The most common types in people with SCLC are:

SCLC and combined SCLC have similar risk factors, such as advanced age, male sex, and smoking history.

The median age range of people who receive a diagnosis of combined SCLC is 59 to 64 years. Males seem to be affected more often than females, possibly as a result of higher rates of smoking.

A history of smoking is by far the top risk factor for developing SCLC. Only about 2% of SCLC cases occur in never-smokers (people who have smoked fewer than 100 cigarettes in their life). Almost all people with combined SCLC have a history of heavy smoking.

The main treatments for SCLC are chemotherapy and radiation therapy. These treatments may be administered:

Surgery is rarely used to treat pure SCLC because the cancer has usually already advanced too far to be removed by the time a doctor diagnoses it. Fewer than 1 in 20 people have SCLC that is isolated to a single tumor and hasn’t spread to another organ or the lymph nodes.

Combined SCLC seems to develop more often in the outer part of the lung and is more often surgically removable. Surgery is usually an option for only limited stage cancer.

Only about 40% of SCLC cases are diagnosed in the limited stage, which is when the cancer is on only one side of the chest and may or may not have spread to nearby lymph nodes on the same side.

More than 70% of cases of combined SCLC seem to be diagnosed in the limited stage.

When chemotherapy is administered, doctors often use the EC/EP regimen, which includes the following drugs:

  • cisplatin
  • etoposide/carboplatin
  • etoposide

Learn more about how limited stage SCLC is treated.

SCLC tends to be more aggressive than NSCLC and generally has a less favorable outlook. Many people do not receive a diagnosis until the cancer has spread to distant tissues.

The American Cancer Society reports the following 5-year relative survival rates for SCLC:

Stage5-year relative survival rate
all stages7%

The 5-year relative survival rate is a measure of how many people with this type of cancer are alive 5 years later compared to people without cancer.

The outlook for combined SCLC tends to be better than for pure SCLC since SCLC seems to be more commonly diagnosed in the early stages. However, tumors with NSCLC components also seem to show stronger resistance to radiation therapy and chemotherapy.

SCLC is less common than the other main category of lung cancer, NSCLC, but tends to be more aggressive. The classification of SCLC has changed over the years, but the newest WHO guidelines classify it as either pure SCLC or combined SCLC. Combined SCLC has some of the same features as NSCLC.

SCLC tends to have a poor outlook and be aggressive. Surgery is usually an option only if the cancer is limited to one lung, which occurs in most people with SCLC.

Your doctor can help you figure out what treatment options may give you the best chances of survival. Your doctor will likely recommend some combination of radiation therapy and chemotherapy.