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How Is Lung Cancer Diagnosed?

Medically reviewed by Todd Gersten, M.D.
Written by Emily Wagner, M.S.
Updated on April 6, 2021

Lung cancers can be difficult to diagnose due to lack of regular screening. Most often, lung cancer is found when symptoms become noticeable. If you believe you are experiencing symptoms of lung cancer, speak with your doctor.

Lung cancer is the second most common cancer for both men and women in the U.S. Most people who are diagnosed with lung cancer are 65 years or older, with few people diagnosed before the age of 45. The two main types of lung cancer are non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC).

The diagnostic process begins with a visit to your doctor. Your doctor will start with a medical history and physical exam to identify possible risk factors for and symptoms of lung cancer. If they find anything during the exam that might suggest lung cancer, more tests will be done.

Imaging Tests

Imaging tests can be used to look inside the lungs to identify if cancer is present and if it has spread. Imaging can be used:

  • To look at suspected areas of cancer
  • To determine if a treatment is effective
  • To see if the cancer has spread
  • To check for possible signs of relapse (cancer growing back after treatment)

Chest X-Ray

A chest X-ray is usually the first imaging test your doctor will perform to look for any abnormal areas or masses in the lung. Images are taken from the front and back of the chest. Chest X-rays have also been studied as a method of lung cancer screening, but they are not as informative as other methods. If your doctor finds something on a chest X-ray, they will often order a computed tomography (CT) scan to confirm the findings.

Computed Tomography Scan

A CT scan uses X-rays to make detailed images of your body at multiple angles. The CT scanner takes many pictures, and then a computer combines them to study the body in more detail.

A CT scan is more likely than a chest X-ray to pick up on lung tumors. It can also show the shape, size, and position of lung tumors and any lymph nodes where the cancer may have spread. In addition to the lungs, CT scans can spot abnormal areas in the liver, brain, adrenal glands, and other organs where lung cancer might metastasize.

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) scans are another technique for generating detailed images of the body. However, MRI scans use strong magnets and radio waves instead of X-rays. They are most often used to look for the spread of lung cancer to the spinal cord or brain.

Positron Emission Tomography Scan

For a positron emission tomography (PET) scan, a slightly radioactive form of sugar is injected into a vein and collects in cancer cells. A PET/CT scan can be used for diagnosing lung cancer. It is not recommended for follow-up scans after treatment. This scan can also detect cancer that has spread to the bones, liver, adrenal glands, and other organs; but it is not useful for looking at the spinal cord or brain.

Bone Scan

Bone scans can spot cancer that may have metastasized from the lungs to the bones. A slightly radioactive material is injected into the blood and collects in the bones over a few hours. Scans are then done to look for areas of higher radioactivity which may indicate cancer.

Lung-Specific Tests

While symptoms and imaging tests can suggest cancer, the only way to definitively diagnose it is by looking at lung cells under a microscope. The cells can be collected from mucus, fluid around the lung, or a tissue biopsy. Depending on the situation, different tests may be necessary to come to a conclusive diagnosis.

Sputum Cytology

Sputum cytology is the analysis of a sample of sputum (mucus) under a microscope to look for cancer cells. The samples are collected early in the morning, three days in a row. Sputum cytology is best for finding cancer types that start in the major airways of the lung, like squamous cell lung cancers. It is possible for sputum cytology tests to be negative even if there is lung cancer, so other tests will be needed.


If there is fluid collecting around the lungs (known as a pleural effusion), your doctor may perform thoracentesis. Fluid buildup can be caused by cancer spread from the lungs to the pleura or by an infection or heart failure.

During the procedure, the skin is numbed and a hollow needle is inserted between the ribs, draining the fluid. The fluid is then sent to a lab to check for cancer cells. Thoracentesis can also be performed to relieve pressure from fluid buildup around the lungs, helping a person breathe better.


Bronchoscopy involves the use of a thin, flexible tube with a light and camera attached to the end (known as a bronchoscope). The tube is inserted through the nose or mouth and travels down into the lungs. This allows doctors to look inside the lungs and airways for any tumors or blockages.

Needle Biopsy

When doctors want to sample tissue to look for cancer, they use a needle biopsy. The area where cancer is suspected is numbed, and a hollow needle is inserted there to remove tissue. The biopsy is then analyzed for cancer cells.

One advantage of needle biopsies is that they are not surgical procedures, and they can be performed relatively quickly. The drawback is that the biopsy only removes a very small tissue sample. In some cases, the sample may not have enough cancerous tissue to tell the doctor everything they need to know.

Fine Needle Aspiration Biopsy

Fine needle aspiration (FNA) biopsies use a very thin, hollow needle to extract cells and small pieces of tissue from the suspected area. A transtracheal or transbronchial FNA can be performed by inserting the needle through the wall of the trachea (windpipe) or bronchi (airways) during an endobronchial ultrasound or bronchoscopy. An FNA biopsy can be used to look for cancer in the lymph nodes between the lungs.

Core Biopsy

A core biopsy requires a larger hollow needle to remove tissue. Core biopsy samples are larger than FNA biopsies and can be better for diagnosing lung cancer. A core biopsy may involve local anesthesia.

Transthoracic Needle Biopsy

A transthoracic needle biopsy is performed if a suspected tumor is in the outer part of the lungs. The area is numbed, and the biopsy needle is inserted through the skin on the chest wall. A CT scan or other imaging method is used to help guide the needle.

Tests for Lung Cancer Spread in the Chest

Several tests may be used to determine if lung cancer has spread beyond the lungs.

Mediastinoscopy and Mediastinotomy

A mediastinoscopy can examine the area behind the breastbone and in between the lungs, known as the mediastinum. The procedure involves the use of a mediastinoscope — a flexible tube with a light, camera, and small cutting tool on the end. The scope is inserted through a small incision just above the breastbone and moved into the mediastinum.

During a mediastinoscopy, lymph nodes along the windpipe and in the major bronchial tube areas can be biopsied or removed to look for cancer. Medianstinoscopy can also be used to stage lung cancer.

If some lymph nodes cannot be reached by mediastinoscopy, a surgeon may perform a mediastinotomy to remove biopsy samples. A slightly larger incision (around 2 inches long) is made between the left second and third ribs next to the breastbone. Then a tube is placed in the incision, allowing the surgeon to take tissue samples.

Endobronchial Ultrasound

An endobronchial ultrasound (EBUS) bronchoscopy is used to diagnose lung cancer, inflammation, or infections. A pulmonologist (lung specialist) uses a bronchoscope to look at your trachea and lungs. EBUS can also examine lymph nodes and other structures between the lungs, allowing the doctor to take biopsies.

Endoscopic Ultrasound

An endoscopic ultrasound (EUS) uses high-frequency sound waves to generate detailed images of the chest and lymph nodes. It can be used to follow up on findings from a CT scan or MRI showing possible cancer. In confirmed cancer cases, EUS can also provide precise information on how deep a tumor is and if the cancer has spread to lymph nodes or other organs.


Doctors can use thoracoscopy to look inside the chest to find out if cancer has spread in the space between the lungs and the chest wall. It can also be used to take tissue samples from the outer parts of the lungs, the lymph nodes, and fluids. A thoracoscopy can be combined with video-assisted thoracic surgery (VATS) to remove tissue in early stage lung cancers.

Genetic Testing

Genetic testing can identify mutations in genes associated with lung cancer, most commonly non-small cell lung cancer. Cancers with these genetic mutations can often be treated with targeted drugs. Examples of commonly mutated genes include:

  • EGFR — Around 10 percent to 20 percent of people with NSCLC have mutated EGFR proteins. This is more common in women, people of Asian descent, and nonsmokers.
  • ALK — Approximately 5 percent of people with NSCLC have a mutation in the ALK gene. This is commonly seen in nonsmokers or light smokers with the adenocarcinoma subtype of NSCLC.
  • ROS1 — Between 1 percent and 2 percent of people with NSCLC have mutations in the ROS1 gene.
  • BRAF — About 5 percent of people with NSCLC have mutations in the BRAF gene.
  • RET or MET — A small percentage of people with NSCLC have mutations in either the RET or MET gene.

Blood Tests

While they do not diagnose lung cancer directly, blood tests can help doctors better understand your general health. The results may determine if you are healthy enough for surgery or other kinds of cancer treatments.

Blood chemistry tests help find abnormalities in organs, like the kidneys or liver. For example, if lung cancer has metastasized to the bones, it may raise the levels of calcium and alkaline phosphatase (an enzyme that breaks down proteins) in your blood.

A complete blood count (CBC) panel looks at the numbers of different blood cells in your body. A CBC can alert your doctors to any abnormalities, such as whether you are susceptible to infections due to a low number of white blood cells. CBC panels may be taken repeatedly during treatment to monitor your blood cell counts, as cancer treatments can affect the blood-forming cells in the bone marrow.

Lung Cancer Condition Guide

Updated on April 6, 2021
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Todd Gersten, M.D. is a hematologist-oncologist at the Florida Cancer Specialists & Research Institute in Wellington, Florida. Review provided by VeriMed Healthcare Network. Learn more about him here.
Emily Wagner, M.S. holds a Master of Science in biomedical sciences with a focus in pharmacology. She is passionate about immunology, cancer biology, and molecular biology. Learn more about her here.

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