Understanding Lung Cancer

How is Lung Cancer Diagnosed?

Last updated and reviewed on May 16, 2026. 

The process of diagnosing lung cancer usually starts when a patient notices something is wrong. Common warning signs include a cough that will not go away, coughing up blood, shortness of breath, chest pain, or repeated lung infections. However, lung cancer does not always cause noticeable symptoms, especially in the early stages. In fact, research shows that less than 10% of patients have no symptoms at all when their cancer is first found, meaning most people do feel something before their diagnosis is made.

When a patient visits their doctor with these kinds of concerns, the first step is a thorough history and physical exam. The doctor will ask about your symptoms, your smoking history, any exposure to harmful chemicals at work, and your family history of cancer. According to the American College of Chest Physicians, this initial evaluation should also include blood tests and imaging of the chest to check for signs of disease. These early steps help the doctor figure out whether more testing is needed and where to look first.

If the physical exam and blood tests raise concerns, the doctor will move on to imaging tests. A chest X-ray is often the first image taken. While an X-ray can show unusual spots in the lungs, it is not detailed enough to tell doctors whether something is cancer. The next step is almost always a low-dose CT scan of the chest, which gives doctors a much clearer and more detailed picture of the lungs, lymph nodes, and nearby organs. If the low-dose CT scan shows something suspicious, doctors will typically then order a biopsy to be sure.

A biopsy is the key step that confirms whether or not cancer is present. During a biopsy, a doctor collects a small piece of tissue from the suspicious area. This sample is then looked at under a microscope by a specialist called a pathologist, who can tell whether the cells are cancerous. The biopsy also shows what type of lung cancer it is, which is critically important because different types of lung cancer are treated in very different ways. Without a biopsy, doctors cannot make a definitive diagnosis.

Once cancer is confirmed, doctors will do additional tests to figure out how far the cancer has spread. This is called staging. Staging guides the treatment plan and gives both the doctor and patient a better sense of what to expect. Your care team may feel like they are ordering a lot of tests, but each one provides important information. The goal is to build the most accurate and complete picture of your cancer so that the treatment plan is tailored specifically to you.

What tests are used to diagnose lung cancer?

Several different types of tests are used to diagnose lung cancer, and doctors often use more than one. The most common tests fall into four main categories:

1. Imaging tests
2. Tissue tests (biopsies)
3. Blood tests
4. Molecular tests.

Understanding what each test does can help reduce some of the anxiety that comes with going through so many procedures.

Imaging Tests create pictures of the inside of your body. The most commonly used imaging test for lung cancer is the low-dose CT scan, also called an LDCT. This scan is so good at finding small nodules in the lungs that it is now recommended as an annual screening test for people between the ages of 50 and 80 who are current or former smokers with at least a 20 pack-year smoking history, according to both the American Cancer Society and the U.S. Preventive Services Task Force. Research shows that LDCT screening can reduce lung cancer deaths by about 20% compared to a standard chest X-ray ¹. A PET-CT scan is another powerful imaging tool that is often used after a suspicious CT finding. A PET scan shows where cancer cells are most active in the body by detecting high energy use, which cancer cells tend to have. When combined with a CT scan, doctors get both a location and an idea of how active the cancer is. This combination is considered better than either test alone for figuring out the extent and stage of the cancer. Brain MRI scans may also be ordered to check whether cancer has spread to the brain.

Biopsies are the most important tests for confirming a lung cancer diagnosis. As mentioned, a biopsy involves removing a small sample of tissue from a suspicious area for examination. There are several ways doctors can do this. A bronchoscopy involves passing a thin, flexible tube with a camera through the nose or mouth and down into the airways, where small tissue samples can be collected. This approach is especially useful for tumors located near the center of the lungs, where bronchoscopic biopsy has been shown to have a sensitivity greater than 95% for detecting early-stage cancer ². For tumors in the outer parts of the lungs, doctors may instead use a needle guided by CT imaging to collect the sample through the chest wall. While this approach is more direct, it does carry a small risk of causing a collapsed lung (pneumothorax). No matter how it is collected, the biopsy tissue sample remains the gold standard for confirming that cancer is present and identifying exactly what type it is.

Blood Tests are used alongside imaging and biopsy, but cannot diagnose lung cancer on their own. Basic blood tests check for general health markers and organ function, which helps doctors understand how well your body is working and plan safe treatment. A newer and exciting type of blood test is called a liquid biopsy. Instead of taking tissue from the lungs, a liquid biopsy looks for fragments of cancer DNA floating in the blood. This is a much less invasive approach, and research shows it can reduce the time from diagnosis to starting treatment. In one study, using liquid biopsy alongside nurse navigation reduced the average time to treatment from 36 days to just 21 days ³. While liquid biopsy is not yet a replacement for tissue biopsy, it is becoming an increasingly important tool, particularly for monitoring how cancer responds to treatment.

Molecular and Genetic Tests are done on the biopsy tissue after cancer has been confirmed. These tests look for specific changes, called mutations, in the genes of the cancer cells. This is important because about 85% of lung cancers are a type called non-small cell lung cancer, and some of these cancers have specific gene mutations, such as changes in the EGFR, ALK, ROS1, or BRAF genes, that make them eligible for targeted therapies. Targeted therapies are medications that attack cancer based on its specific genetic fingerprint. As of 2024, the FDA has approved 34 targeted therapies for lung cancer. Molecular testing is now a standard part of the diagnostic process, and your doctor will likely recommend it for all newly diagnosed patients to help find the best treatment option for your specific cancer.

It is normal to feel overwhelmed by how many tests are involved in diagnosing lung cancer. But each test answers a specific question and adds to your care team's understanding of your unique situation. The more information they have, the better equipped they are to build a treatment plan that is right for you. Do not hesitate to ask your doctor to explain any test before it happens and what they expect to learn from it.