Diagnosing lung cancer involves a series of tests and procedures designed to identify the disease, determine its type, and assess how far it has spread. Early detection through screening and proper diagnostic testing can significantly impact treatment options and outcomes for people at risk.

Introduction: Who Should Undergo Diagnostics

If you’re experiencing symptoms that might suggest lung cancer, it’s important to see your doctor as soon as possible. The most common symptom of lung cancer is a persistent cough that doesn’t go away, but this alone doesn’t mean you have cancer since coughing can have many causes. However, when a persistent cough is accompanied by other warning signs, you should seek medical attention promptly.^[1]

You should consider consulting a healthcare professional if you develop symptoms including coughing up blood, even a small amount, persistent breathlessness, unexplained tiredness and weight loss, or an ache or pain when breathing or coughing. These symptoms can also include chest pain, hoarseness, shortness of breath, or wheezing.^[1][2]

It’s important to understand that lung cancer typically doesn’t cause noticeable symptoms until it has spread through the lungs or into other parts of the body. This is why screening is so valuable for people at high risk.^[6]

Even if you don’t have symptoms, you should undergo diagnostic screening if you fall into certain high-risk categories. People between 50 and 80 years of age who have smoked heavily—specifically those with a 20 pack-year smoking history who currently smoke or have quit within the past 15 years—should have annual screening using low-dose CT scans, which are special types of X-rays that use less radiation than standard CT scans.^[7][12]

If you smoke and haven’t been able to quit, make an appointment with your healthcare provider. They can recommend strategies for quitting smoking, which may include counseling, medicines, and nicotine replacement products. Quitting smoking is important not only for prevention but also if you’re already diagnosed with lung cancer, as it can improve treatment outcomes.^[2]

Classic Diagnostic Methods

When lung cancer is suspected, your healthcare team will use a variety of tests to confirm whether cancer is present, identify what type it is, and determine how advanced it might be. The diagnostic process usually begins with simpler tests and moves to more complex ones as needed.

Initial Evaluation and Imaging Tests

The initial evaluation for lung cancer typically begins with a detailed medical history and physical examination. Your doctor will ask about your smoking history, environmental and work exposures, and any symptoms you’re experiencing. This information helps determine your risk level and guides which tests should be performed.^[12]

Laboratory testing is an important early step. This usually includes a complete blood count, serum chemistries to check how your organs are functioning, calcium levels, and liver function tests. These blood tests help your doctor understand your overall health and can sometimes reveal abnormalities that suggest cancer has spread.^[12]

Imaging tests are used to create pictures of the inside of your body, showing the location and size of any lung cancer. A chest X-ray is often the first imaging test performed. However, when there’s a high level of suspicion for lung cancer, a CT scan (computed tomography scan) of the chest with intravenous contrast media should be performed, even if the X-ray results appear normal. CT scans provide much more detailed images than regular X-rays and can detect smaller abnormalities.^[7][12]

Additional imaging tests may include MRI scans (magnetic resonance imaging), which use magnets and radio waves instead of radiation to create detailed pictures of soft tissues in your body. PET scans (positron emission tomography) may also be used—these are specialized nuclear scans that can help determine if abnormal areas seen on other imaging tests are actually cancer and whether the cancer has spread to other parts of your body.^[7]

Sputum Testing

Sputum is the mucus that is coughed up from your lungs. If you are coughing up sputum, it can be examined under a microscope in a laboratory. This test, called sputum cytology, can sometimes show lung cancer cells. However, sputum testing alone is not usually enough to diagnose lung cancer—other tests are typically needed to confirm the diagnosis.^[7]

Biopsy Procedures

A biopsy is a procedure to remove a sample of tissue for testing in a laboratory. This is the most definitive way to diagnose lung cancer because it allows doctors to examine the actual cells and determine whether they are cancerous and, if so, what type of cancer it is. There are several different ways to obtain a biopsy sample, and your doctor will choose the method based on where the suspected cancer is located and your overall health.^[7]

Bronchoscopy is a common procedure used to diagnose lung cancer. During a flexible bronchoscopy, a healthcare professional inserts a thin, bendable tube called a bronchoscope through your mouth or nose into your lungs. The bronchoscope has a light and a small camera that allow the doctor to look inside your lungs’ airways. Small tools can be passed through the bronchoscope to take tissue samples from suspicious areas.^[7]

If the suspicious area is located near the edge of the lung or outside the airways, other biopsy techniques may be used. A fine-needle aspiration involves inserting a thin needle through the chest wall to remove a small sample of tissue. This is usually done with guidance from CT imaging to ensure the needle reaches the correct location. Mediastinoscopy is a surgical procedure where a small incision is made at the base of the neck, and a thin, lighted tube is used to examine the area between the lungs and take samples from lymph nodes.^[12]

If fluid has built up around the lungs—a condition called pleural effusion—a procedure called thoracentesis may be performed. During this procedure, a needle is inserted through the chest wall to remove fluid, which can then be tested for cancer cells.^[12]

Determining Cancer Type and Stage

Once cancer cells are confirmed, laboratory specialists examine them under a microscope to determine the type of lung cancer. The two main types are non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Non-small cell lung cancer is the most common type, accounting for more than 80% of lung cancer cases. It includes several subtypes such as adenocarcinoma, squamous cell carcinoma, and large cell carcinoma.^[1][3]

Small cell lung cancer grows more quickly and is harder to treat than non-small cell lung cancer. It’s often found as a relatively small lung tumor that has already spread to other parts of the body by the time it’s diagnosed. The cancer cells in small cell lung cancer look small when examined under a microscope, which is how this type gets its name.^[1]

After the type of lung cancer is identified, additional tests are done to determine the stage of the cancer—that is, how large it is and whether it has spread. This process is called staging. Staging helps doctors understand how advanced the cancer is and guides treatment decisions. The stage is based on the size of the initial tumor, how far or deep into surrounding tissue it goes, and whether it has spread to lymph nodes or other organs.^[1]

Lung cancer is generally staged from 0 to IV (4). Stage 0, also called carcinoma in situ, means cancer is in the top lining of the lung or bronchus and hasn’t spread. Stage I means cancer hasn’t spread outside the lung. As the stages progress, the cancer is larger or has spread to lymph nodes or other structures. Stage IV means the cancer has spread to the other lung, the fluid around the lung or heart, or distant organs.^[1]

Diagnostics for Clinical Trial Qualification

Clinical trials are research studies that test new treatments to see if they are safe and effective. If you have lung cancer, you may want to participate in a clinical trial, which can give you access to cutting-edge treatments that aren’t yet widely available. However, to join a clinical trial, you must meet certain requirements, and specific diagnostic tests are used to determine whether you qualify.^[9]

Biomarker Testing

One of the most important diagnostic procedures for qualifying for clinical trials is biomarker testing, also called genetic testing or molecular testing. If you have lung cancer, especially non-small cell lung cancer, your doctor may run tests to find out if you have a change in your genes, known as a genetic mutation. These mutations occur in the cancer cells themselves, not in your inherited genes, so they won’t be passed on to your children.^[9]

The results of biomarker testing help your doctor determine which treatments will work best for you. Many newer treatments, called targeted therapies, are designed to work on cancers with specific genetic mutations. Clinical trials often test these targeted therapies and require participants to have particular mutations before they can enroll. Some targeted therapies have been approved for use based on specific biomarkers, while others are still being studied in trials.^[9]

Biomarker testing requires a sample of your cancer tissue, which is usually obtained during a biopsy. The tissue is sent to a specialized laboratory where scientists look for specific mutations or other molecular characteristics. This testing can take several days to a few weeks to complete, but the information it provides is crucial for matching you with the most appropriate clinical trials and treatments.

Staging and Performance Status

Clinical trials typically have specific requirements about the stage of cancer they will accept. Some trials are designed for early-stage cancers, while others focus on advanced or metastatic disease—cancer that has spread to other parts of the body. The staging tests described earlier, including imaging studies and biopsies, are used to determine whether your cancer stage matches what the trial is studying.^[9]

Many clinical trials also require assessment of your overall health and ability to carry out daily activities. This is often measured using something called performance status, which is a standardized way of describing how cancer and its symptoms affect your daily living abilities. Your doctor will evaluate this as part of determining your eligibility for specific trials.

Baseline Health Assessment

Before you can join a clinical trial, you’ll undergo comprehensive testing to establish your baseline health status. This typically includes all the standard diagnostic tests already mentioned—blood tests, imaging studies, and tissue analysis—but may also include additional specialized tests depending on what the trial is studying. These baseline tests serve several purposes: they help determine if you’re healthy enough to safely participate in the trial, they provide a starting point for measuring how well the treatment works, and they help researchers understand any side effects that might occur.^[9]

The specific tests required vary widely depending on the clinical trial. Some trials test new imaging techniques or diagnostic tools themselves, in which case you might undergo experimental diagnostic procedures as part of the trial. Other trials may require more frequent monitoring with standard tests to carefully track how the cancer responds to treatment and watch for any safety concerns.