What is small cell lung cancer? 

Small cell lung cancer (SCLC) is a type of lung cancer that usually starts in cells involved in air and blood flow in the lungs and airways. In small cell lung cancer, these cells begin growing and dividing faster than they should, forming a tumor. These cancer cells can also spread (metastasize) to other parts of the body more quickly than other types of lung cancer. 

Around 15% of lung cancers are small cell lung cancer. It is called “small cell” because, under a microscope, the cancer cells look very small and not like normal lung cells. These cells can grow and spread faster than other types of lung cancer. Because of this, healthcare teams will usually want to start treatment as soon as possible. 

Small cell lung cancer often begins near the center of the chest and may have already spread beyond the lungs by the time it is diagnosed, which can cause other symptoms.  

What causes SCLC? 

The most common cause of small cell lung cancer is smoking or exposure to tobacco smoke. However, some people who have never smoked can develop small cell lung cancer. Other factors that increase the risk include: 

• Being over 70 years old. 
• Previous radiation therapy to the chest. 
• Exposure to certain chemicals (carcinogens), such as asbestos. 

Doctors do not need to know why someone has developed small cell lung cancer to decide on the most appropriate treatment. Even when the cause is not known, doctors can still determine the best treatment plan based on the stage of the cancer, overall health, and other factors. 

References

1. Cancer Research UK. Types of lung cancer. https://www.cancerresearchuk.org/about-cancer/lung-cancer/stages-types/types. Updated Jan 13, 2026. Accessed Feb 19, 2026. 

2. Cancer Research UK. What are lung neuroendocrine cancers? https://www.cancerresearchuk.org/about-cancer/neuroendocrine-tumours-nets/types/lung-nets/what-are-lung-nets. Updated Feb 14, 2025. Accessed Feb 19, 2026. 

3. National Comprehensive Cancer Network® (NCCN®). NCCN guidelines for patients: Small cell lung cancer, 2024. https://www.nccn.org/patients/guidelines/content/PDF/SCLC-patient-guideline.pdf. Accessed Feb 19, 2026 

4. American Cancer Society. Key statistics for lung cancer. https://www.cancer.org/cancer/types/lung-cancer/about/key-statistics.html. Updated Jan 13, 2026. Accessed Feb 19, 2026. 

5. National Cancer Institute. NCI dictionary of terms small cell lung cancer. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/small-cell-lung-cancer. Accessed Feb 19, 2026. 

6. Macmillan Cancer Support. Small cell lung cancer (SCLC). https://www.macmillan.org.uk/cancer-information-and-support/lung-cancer/small-cell-lung-cancer. Accessed Feb 19, 2026.