Some lung cancers can be found by screening, but most lung cancers are found because they are causing problems. The actual diagnosis of lung cancer is made by looking at a sample of lung cells in the lab. If you have possible signs or symptoms of lung cancer, see your doctor.

Medical history and physical exam

Your doctor will ask about your medical history to learn about your symptoms and possible risk factors. Your doctor will also examine you to look for signs of lung cancer or other health problems.

If the results of your history and physical exam suggest you might have lung cancer, more tests will be done. These could include imaging tests and/or biopsies of the lung.

Imaging tests to look for lung cancer

Imaging tests use x-rays, magnetic fields, sound waves, or radioactive substances to create pictures of the inside of your body. Imaging tests might be done for a number of reasons both before and after a diagnosis of lung cancer, including:

• To look at suspicious areas that might be cancer
• To learn how far cancer might have spread
• To help determine if treatment is working
• To look for possible signs of cancer coming back after treatment

Chest x-ray

A chest x-ray is often the first test your doctor will do to look for any abnormal areas in the lungs. If something suspicious is seen, your doctor may order more tests.

Computed tomography (CT) scan

A CT scan uses x-rays to make detailed cross-sectional images of your body. Instead of taking 1 or 2 pictures, like a regular x-ray, a CT scanner takes many pictures and a computer then combines them to show a slice of the part of your body being studied.

A CT scan is more likely to show lung tumors than routine chest x-rays. It can also show the size, shape, and position of any lung tumors and can help find enlarged lymph nodes that might contain cancer that has spread. This test can also be used to look for masses in the adrenal glands, liver, brain, and other organs that might be due to the lung cancer spread.

CT-guided needle biopsy: If a suspected area of cancer is deep within your body, a CT scan might be used to guide a biopsy needle into this area to get a tissue sample to check for cancer.

Magnetic resonance imaging (MRI) scan

Like CT scans, MRI scans show detailed images of soft tissues in the body. But MRI scans use radio waves and strong magnets instead of x-rays. MRI scans are most often used to look for possible spread of lung cancer to the brain or spinal cord.

Positron emission tomography (PET) scan

For a PET scan, a slightly radioactive form of sugar (known as FDG) is injected into the blood and collects mainly in cancer cells.

PET/CT scan: Often a PET scan is combined with a CT scan using a special machine that can do both at the same time. This lets the doctor compare areas of higher radioactivity on the PET scan with a more detailed picture on the CT scan. This is the type of PET scan most often used in patients with lung cancer.

PET/CT scans can be useful:

• If your doctor thinks the cancer might have spread but doesn’t know where. They can show spread of cancer to the liver, bones, adrenal glands, or some other organs. They are not as useful for looking at the brain or spinal cord.
• In diagnosing lung cancer, but their role in checking whether treatment is working is unproven. Most doctors do not recommend PET/CT scans for routine follow up of patients after lung cancer treatment.

Bone scan

For a bone scan, a small amount of low-level radioactive material is injected into the blood and collects mainly in abnormal areas of bone. A bone scan can help show if a cancer has spread to the bones. But this test isn’t needed very often because PET scans can usually show if cancer has spread to the bones.

Tests to diagnose lung cancer

Symptoms and the results of certain tests may strongly suggest that a person has lung cancer, but the actual diagnosis is made by looking at lung cells in the lab.

The cells can be taken from lung secretions (mucus you cough up from the lungs), fluid removed from the area around the lung (thoracentesis), or from a suspicious area using a needle or surgery (biopsy). The choice of which test(s) to use depends on the situation.

Sputum cytology

A sample of sputum (mucus you cough up from the lungs) is looked at in the lab to see if it has cancer cells. The best way to do this is to get early morning samples 3 days in a row. This test is more likely to help find cancers that start in the major airways of the lung, such as squamous cell lung cancers. It might not be as helpful for finding other types of lung cancer. If your doctor suspects lung cancer, further testing will be done even if no cancer cells are found in the sputum.

Thoracentesis

If fluid has collected around the lungs (called a pleural effusion), doctors can remove some of the fluid to find out if it is caused by cancer spreading to the lining of the lungs (pleura). The buildup might also be caused by other conditions, such as heart failure or an infection.

For a thoracentesis, the skin is numbed and a hollow needle is inserted between the ribs to drain the fluid. The fluid is checked in the lab for cancer cells. Other tests of the fluid are also sometimes useful in telling a malignant (cancerous) pleural effusion from one that is not.

If a malignant pleural effusion has been diagnosed and is causing trouble breathing, a thoracentesis may be repeated to remove more fluid which may help a person breathe better.

Needle biopsy

Doctors often use a hollow needle to get a small sample from a suspicious area (mass). An advantage of needle biopsies is that they don’t require a surgical incision. The drawback is that they remove only a small amount of tissue and in some cases, the amount of tissue removed might not be enough to both make a diagnosis and to perform more tests on the cancer cells that can help doctors choose anticancer drugs.

Fine needle aspiration (FNA) biopsy

The doctor uses a syringe with a very thin, hollow needle to withdraw (aspirate) cells and small fragments of tissue. A FNA biopsy may be done to check for cancer in the lymph nodes between the lungs.

Transtracheal FNA or transbronchial FNA is done by passing the needle through the wall of the trachea (windpipe) or bronchi (the large airways leading into the lungs) during bronchoscopy or endobronchial ultrasound (described below).

In some patients an FNA biopsy is done during an endoscopic esophageal ultrasound (described below) by passing the needle through the wall of the esophagus.

Core biopsy 

A larger needle is used to remove one or more small cores of tissue. Samples from core biopsies are often preferred because they are larger than FNA biopsies.

Transthoracic needle biopsy

If the suspected tumor is in the outer part of the lungs, the biopsy needle can be put through the skin on the chest wall. The area where the needle is to be inserted may be numbed with local anesthesia first. The doctor then guides the needle into the area while looking at the lungs with either fluoroscopy (which is like an x-ray) or a CT scan.

A possible complication of this procedure is that air may leak out of the lung at the biopsy site and into the space between the lung and the chest wall. This is called a pneumothorax. It can cause part of the lung to collapse and sometimes trouble breathing. If the air leak is small, it often gets better without any treatment. Large air leaks are treated by inserting a chest tube (a small tube into the chest space) which sucks out the air over a day or two, after which it usually heals on its own.

Bronchoscopy

Bronchoscopy can help the doctor find some tumors or blockages in the larger airways of the lungs, which can often be biopsied during the procedure.

Tests to look for lung cancer spread in the chest

If lung cancer has been found, it’s often important to know if it has spread to the lymph nodes in the space between the lungs (mediastinum) or other nearby areas. This can affect a person’s treatment options. Several types of tests can be used to look for this cancer spread.

Endobronchial ultrasound

An endobronchial ultrasound can be used to see the lymph nodes and other structures in the area between the lungs if biopsies need to be taken in those areas.

Endoscopic esophageal ultrasound

An endoscopic esophageal ultrasound goes down into the esophagus where it can show the nearby lymph nodes which may contain lung cancer cells. Biopsies of the abnormal lymph nodes can be taken at the same time as the procedure.

Mediastinoscopy and mediastinotomy

These procedures may be done to look more directly at and get samples from the structures in the mediastinum (the area between the lungs). The main difference between the two is in the location and size of the incision.

A mediastinoscopy is a procedure that uses a lighted tube inserted behind the sternum (breast bone) and in front of the windpipe to look at and take tissue samples from the lymph nodes along the windpipe and the major bronchial tube areas. If some lymph nodes can’t be reached by mediastinoscopy, a mediastinotomy may be done so the surgeon can directly remove the biopsy sample. For this procedure, a slightly larger incision (usually about 2 inches long) between the left second and third ribs next to the breast bone is needed.

Thoracoscopy

Thoracoscopy can be done to find out if cancer has spread to the spaces between the lungs and the chest wall, or to the linings of these spaces. It can also be used to sample tumors on the outer parts of the lungs as well as nearby lymph nodes and fluid, and to assess whether a tumor is growing into nearby tissues or organs. This procedure is not often done just to diagnose lung cancer, unless other tests such as needle biopsies are unable to get enough samples for the diagnosis. Thoracoscopy can also be used as part of the treatment to remove part of a lung in some early-stage lung cancers. This type of operation, known as video-assisted thoracic surgery (VATS), is described in Surgery for Non-Small Cell Lung Cancer.

Lung function tests

Lung (or pulmonary) function tests (PFTs) are often done after lung cancer is diagnosed to see how well your lungs are working. This is especially important if surgery might be an option in treating the cancer. Surgery to remove lung cancer may mean removing part or all of a lung, so it’s important to know how well your lungs are working beforehand. Some people with poor lung function (like those with lung damage from smoking) don’t have enough undamaged lung to withstand removing even part of a lung. These tests can give the surgeon an idea of whether surgery is a good option, and if so, how much lung can safely be removed.

There are different types of PFTs, but they all basically have you breathe in and out through a tube that is connected to a machine that measures airflow.

Sometimes PFTs are coupled with a test called an arterial blood gas. In this test, blood is removed from an artery (instead of from a vein, like most other blood tests) so the amount of oxygen and carbon dioxide can be measured.

Lab tests of biopsy and other samples

Samples that have been collected during biopsies or other tests are sent to a pathology lab. A pathologist, a doctor who uses lab tests to diagnose diseases such as cancer, will look at the samples and may do other special tests to help better classify the cancer. (Cancers from other organs also can spread to the lungs. It’s very important to find out where the cancer started, because treatment is different depending on the type of cancer.)

The results of these tests are described in a pathology report, which is usually available within a week. If you have any questions about your pathology results or any diagnostic tests, talk to your doctor. If needed, you can get a second opinion of your pathology report by having your tissue samples sent to a pathologist at another lab.

For more information, see Understanding Your Pathology Report.

Molecular tests for gene changes

In some cases, especially for non-small cell lung cancer (NSCLC), doctors may test for specific gene changes in the cancer cells that could mean certain targeted drugs might help treat the cancer. For example:

• About 20 -25% of NSCLCs have changes in the KRAS gene that cause them to make an abnormal KRAS protein which helps the cancer cells grow and spread. NSCLCs with this mutation are often adenocarcinomas, resistant to other drugs such as EGFR inhibitors, and are most often found in people with a smoking history.
• EGFR is a protein that appears in high amounts on the surface of 10% to 20% of NSCLC cells and helps them grow. Some drugs that target EGFR can be used to treat NSCLC with changes in the EGFR gene, which are more common in certain groups, such as those who don't smoke, women, and Asians. But these drugs don’t seem to be as helpful in patients whose cancer cells have changes in the KRAS gene.
• About 5% of NSCLCs have a change in the ALK gene. This change is most often seen in people who don't smoke (or who smoke lightly) who have the adenocarcinoma subtype of NSCLC. Doctors may test cancers for changes in the ALK gene to see if drugs that target this change may help them.
• About 1% to 2% of NSCLCs have a rearrangement in the ROS1 gene, which might make the tumor respond to certain targeted drugs.
• A small percentage of NSCLCs have changes in the RET gene. Certain drugs that target cells with RET gene changes might be options for treating these tumors.
• About 5% of NSCLCs have changes in the BRAF gene. Certain drugs that target cells with BRAF gene changes might be an option for treating these tumors.
• A small percentage of NSCLCs have certain changes in the MET gene that make them more likely to respond to some targeted drugs.
• In a small percentage of NSCLCs, the cancer cells have certain changes in the HER2 gene that make them more likely to respond to a targeted drug.
• A small number of NSCLCs have changes in one of the NTRK genes that make them more likely to respond to some targeted drugs.

These molecular tests can be done on tissue taken during a biopsy or surgery for lung cancer. If the biopsy sample is too small and all the molecular tests cannot be done, the testing may also be done on blood that is taken from a vein just like a regular blood draw. This blood contains the DNA from dead tumor cells found in the bloodstream of people with advanced lung cancer. Obtaining the tumor DNA through a blood draw is sometimes called a liquid biopsy and can have advantages over a standard needle biopsy, which can carry risks like a pneumothorax (lung collapse) and shortness of breath.

Tests for certain proteins on tumor cells

Lab tests might also be done to look for certain proteins on the cancer cells. For example, NSCLC cells might be tested for the PD-L1 protein, which can show if the cancer is more likely to respond to treatment with certain immunotherapy drugs. 

Blood tests

Blood tests are not used to diagnose lung cancer, but they can help to get a sense of a person’s overall health. For example, they can be used to help determine if a person is healthy enough to have surgery.

A complete blood count (CBC) looks at whether your blood has normal numbers of different types of blood cells. For example, it can show if you are anemic (have a low number of red blood cells), if you could have trouble with bleeding (due to a low number of blood platelets), or if you are at increased risk for infections (because of a low number of white blood cells). This test could be repeated regularly during treatment, as many cancer drugs can affect blood-forming cells of the bone marrow.

Blood chemistry tests can help find abnormalities in some of your organs, such as the liver or kidneys. For example, if cancer has spread to the bones, it might cause higher than normal levels of calcium and alkaline phosphatase.