Diagnosing small cell lung cancer 

Most people who are diagnosed with small cell lung cancer (SCLC) see their GP or primary care doctor because they have noticed symptoms. A clinician will take a detailed history and ask about health conditions and lifestyle. Sometimes, small cell lung cancer is found after doctors notice something abnormal on an X-ray or computed tomography (CT) scan done for another reason. 

Not all of the tests described below will be needed for everyone. 

Physical examination 

A doctor will examine the patient and listen to their chest. They may also ask the patient to breathe into a small device called a spirometer to find out more about how well their lungs are working. 

Imaging 

Imaging tests are painless, non-invasive procedures, used to capture pictures of the inside of a patient’s body. A radiologist will interpret these images and look for any abnormalities. Examples of imaging tests used in the diagnosis of small cell lung cancer include:  

• An X-ray, which uses low-dose radiation to take a picture of the inside of the body. 
• A CT (or CAT) scan, which uses X-ray techniques to create detailed 3D images. 
• A positron emission tomography (PET) scan, which uses a small amount of radioactive sugar to help identify areas of active cancer in the body.  

Biopsy 

A biopsy involves taking a sample of tissue from a suspected tumor, which is then sent for laboratory tests. It can be done in several ways: 

• A needle biopsy, where a very fine needle is passed into the lung to remove a sample of tissue or fluid. 
• A bronchoscopy, which uses a thin tube with a light and lens (a bronchoscope) to look inside the airways. Tissue samples can also be taken during the procedure. 
• A thoracoscopy or mediastinoscopy are surgical procedures that allow doctors to look inside the chest and take samples. 
• An endobronchial ultrasound (EBUS) biopsy, which uses a thin bronchoscope with an ultrasound probe to view the airways and nearby lymph nodes, and take tissue samples. 

Laboratory tests 

Tissue or blood samples can be examined using several techniques, including: 

• Microscopy, where cells are examined under a microscope to look for abnormal changes. 
• Immunohistochemistry (IHC), which uses antibodies to identify specific markers of cancer and help confirm whether the cells are small cell lung cancer. 
• Tests to measure the amount of particular substances (biomarkers) in the blood, which may help distinguish small cell lung cancer from other types of cancer, including non-small cell lung cancer. 
• Measuring additional IHC or genetic biomarkers to help predict how well therapies will work.  

Further tests 

If someone is diagnosed with small cell lung cancer, further imaging may be performed to see whether the cancer has spread. These tests help doctors understand the stage of the cancer and plan the most appropriate treatment. They can include: 

• Magnetic resonance imaging (MRI), which uses magnets and radio waves to make detailed pictures of areas inside the body. 
• A bone scan, to see if the cancer has spread to the bones. A small amount of accumulated radioactive material is injected into the blood, and a camera then scans the body and detects if the material has collected anywhere. 

References

1. Macmillan Cancer Support. Small cell lung cancer (SCLC). https://www.macmillan.org.uk/cancer-information-and-support/lung-cancer/small-cell-lung-cancer. Updated Jan 31, 2025. Accessed Mar 3, 2026. 

2. 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 Mar 3, 2026.  

3. Cancer Research UK. Seeing your GP when you have symptoms of lung cancer. https://www.cancerresearchuk.org/about-cancer/lung-cancer/metastatic/symptoms. Updated Oct 7, 2025. Accessed Mar 3, 2026. 

4. Macmillan Cancer Support. X-ray. https://www.macmillan.org.uk/cancer-information-and-support/diagnostic-tests/x-ray. Updated Jan 24, 2022. Accessed Mar 3, 2026. 

5. Cancer Research UK. X-rays. https://www.cancerresearchuk.org/about-cancer/tests-and-scans/x-rays. Updated May 23, 2025. Accessed Mar 3, 2026.

6. Macmillan Cancer Support. CT scan. https://www.macmillan.org.uk/cancer-information-and-support/diagnostic-tests/ct-scan. Updated Jan 24, 2022. Accessed Mar 3, 2026. 

7. Cancer Research UK. Tests for lung cancer. https://www.cancerresearchuk.org/about-cancer/lung-cancer/getting-diagnosed/tests-for-lung-cancer. Updated Oct 8, 2025. Accessed Mar 3, 2026. 

8. National Cancer Institute. Small Cell Lung Cancer Treatment (PDQ®)–Patient Version. https://www.cancer.gov/types/lung/patient/small-cell-lung-treatment-pdq. Updated May 8, 2025. Accessed Mar 3, 2026.