Small cell lung cancer (SCLC) is a less common but more aggressive form of lung cancer than its counterpart, non-small cell lung cancer (NSCLC).

This article will explore the difference between these types of lung cancer, how they spread, and why SCLC moves so much quicker.

Doctors use stages to describe how much cancer has progressed and whether it has spread (metastasized) to other parts of the body. Doctors stage lung cancer using a combination of lab tests, imaging, and physical examinations.

Both SCLC and NSCLC begin in the lungs and can spread to other parts of the body.

But SCLC tends to spread more quickly. Because these cancer cells spread so early and aggressively, the cancer is often already at a more advanced stage by the time doctors detect it.

NSCLC is the more common form of lung cancer. Doctors usually stage NSCLC using numbers, with stage 0 being the most limited stage and stage 4 being the most advanced. With SCLC, doctors usually use only two stages.

Limited stage

Limited stage SCLC is less advanced. Cancer in this stage should only be located on one side of your chest and should be contained within a single treatment area.

This means the cancer is usually in only a small section of one lung, although there may be some spread to the lymph nodes on the same side of the affected lung.

SCLC is not only fast-moving but also difficult to detect in the early stages. Only about 1 in 3 people receive a diagnosis of SCLC in the limited stage.

Extensive stage

Extensive stage SCLC is cancer that has already spread widely through one entire lung, to both lungs, or to areas outside of the lungs. Doctors also consider cancers that have moved into the fluid that surrounds your lungs to be in the extensive stage.

About 2 out of 3 people with SCLC are in the extensive stage when their cancer is first detected.

Doctors often measure cancer growth by the mitotic rate of a particular type of cancer cell. This rate measures how quickly that particular cancer cell divides and multiplies. A higher mitotic rate, or MR, usually corresponds with a lower survival rate.

According to a 2021 review, the average MR of SCLC is 40 mitoses per square millimeter. That means that for each square millimeter of SCLC, 40 cancer cells are actively dividing. To compare, an older study on MRs for NSCLC noted an average rate of 2.1 mitoses per square millimeter.

An easier way to understand what that means for how quickly your cancer is growing is by looking at the doubling time. This figure measures the time it takes for one cell to divide, or a group of cells to double in size. While a higher MR means faster growth, a lower doubling time also means faster growth.

SCLC has a doubling time of 86 days, but it can range from 25 to 217 days, according to a 2020 study. By contrast, a 2019 study of people with NSCLC recorded a median doubling time of 230 days.

There’s no set time for SCLC to progress from limited stage to extensive stage.

SCLC is notorious for its quick spread. Research suggests that long-term exposure to carcinogens, like tobacco smoke, creates genetic mutations. These mutations and other changes from strong carcinogen exposure result in a faster-than-usual doubling time.

Aside from SCLC, the other fastest growing cancer is melanoma, which also develops from exposure to a strong carcinogen (ultraviolet light).

If the area affected by your cancer is small enough, surgical removal may be an option. But in many cases of SCLC at diagnosis, the cancer has already spread too far for surgery to be effective.

When extensive stage SCLC is the diagnosis, first-line treatment may be:

Keep in mind that the goals of treating extensive stage SCLC are to shrink the cancer or slow its growth, reduce your symptoms, and possibly extend your life.

However, due to the advanced stage of these cancers, treatment of extensive stage SCLC is not designed with the hope of removing your cancer completely.

The overall 5-year survival rate for people with SCLC across all stages is about 7 percent. This means that about 7 out of every 100 people with this condition will still be alive 5 years after their initial diagnosis. Your individual outlook will depend on several factors, including:

  • your overall health
  • other medical conditions you may have
  • what treatments you can have
  • the stage of your cancer

People with limited or early stage cancers have better survival rates. SCLC that has not spread outside of the lung has a 5-year survival rate of about 29 percent. These cancers are also more likely to be treated with surgery in addition to chemotherapy and radiation.

SCLC that has spread outside the lungs has a 5-year survival rate of between 3 and 18 percent, depending on the extent of the spread.

Surgery is rarely an option for these cancers. Chemotherapy and radiation are typically palliative, which means they help relieve symptoms or slow the spread of your cancer rather than cure it.

Where does SCLC spread?

SCLC usually begins in your central airways, but it usually spreads first to areas like your:

  • brain
  • liver
  • adrenal glands
  • bone
  • bone marrow

How does a doctor test to see where SCLC has spread?

You will undergo several tests to evaluate the stage and spread of your cancer. These tests may include:

How do I know if I’m at high risk for SCLC?

There are several risk factors for SCLC, but smoking cigarettes is the biggest. Other risk factors include exposure to:

  • second-hand smoke
  • asbestos
  • radon

SCLC is a type of cancer that begins in the lungs and can quickly spread to other areas of the body. SCLC is more difficult to detect in its early stages, so it’s usually more advanced when diagnosed than NSCLC.

When doctors spot most cases, most treatments cannot eliminate your cancer. They can only attempt to reduce your symptoms or slow the spread.

Talk with a doctor about screening for SCLC and other cancers if you have known risk factors, such as a history of smoking.