How Lung Cancer Is Diagnosed

A correct diagnosis is essential to delivering timely and effective lung cancer treatment. Healthcare providers use a variety of tests, such as computed tomography (CT) scans, positron emission tomography (PET) scans, and biopsies, to diagnose the disease.

This article discusses the types of lung cancer and tests commonly used to make a diagnosis. It explains who should be screened for lung cancer and what the results of any tests typically mean.

Physical Examination

When lung cancer is suspected, a healthcare provider will perform a thorough history and physical exam. This is done to evaluate risk factors, such as radon exposure or a smoking history.

It also is used to investigate symptoms of lung cancer, such as a cough or unexplained weight loss.

Other findings from the exam may include:

• Abnormal lung sounds
• Enlarged lymph nodes
• Clubbing of the fingernails (chubby fingernails)
  

Imaging

Your healthcare provider may want imaging studies done. This will depend on the specific symptoms and findings of your exam. These tests may include chest X-ray, CT scan, and other imaging.

Chest X-Ray

When lung cancer is suspected, the first test done is usually a chest X-ray. This may show a mass of abnormal cells in the lungs, or a smaller spot called a lung nodule. Lymph nodes, which are a key part of your immune system, may appear enlarged on an X-ray.

For perspective, a spot on the lung is considered a lung nodule when it is 3 centimeters (1.5 inches) or less in diameter. A lung mass refers to an abnormality that is larger than 3 centimeters in diameter.

Sometimes the chest X-ray is normal and further tests are needed to look for lung cancer. Or, a shadow on a lung X-ray could mean there is a spot on the lung. It also could be a normal part of a person's chest.

Even if a mass does appear on X-ray, it may be benign and not related to lung cancer. Your healthcare provider will want additional tests to confirm any diagnosis.

A chest X-ray alone is not enough to rule out lung cancer. In fact, about 90% of missed lung cancer diagnoses are due to a reliance on chest X-rays.

CT Scan

A CT scan is frequently done to follow up on an abnormal chest X-ray finding. Even when chest X-ray findings are normal, it can be used to further evaluate symptoms that may be associated with lung cancer.

CT scans are done by using a series of X-rays to create a three-dimensional view of the lungs. This approach allows your healthcare team to look at the lungs from more than one angle.

If the CT is abnormal, the diagnosis of lung cancer will still need to be confirmed. This is done through a biopsy, which is used to examine a sample of lung tissue.

MRI

For some people, magnetic resonance imaging (MRI) will be used to evaluate the possibility of lung cancer. The MRI can deliver high-quality images of what's going on inside the body.

It's based on a process that uses radio waves and a magnetic field to create the images. For this reason, some people may need to avoid having an MRI.

They include people with older metal implants, such as heart pacemakers, although newer devices are designed to be safe for MRIs.

PET Scan

A positron emission tomography (PET scan) uses radioactive material approved for medical use. A PET scan will create a colorful, three-dimensional image of the lungs.

What's different is that a PET scan is used to evaluate a tumor, or tumors, that are actively growing. PET scans also can help to show the difference between tumors and scar tissue in people who have scarring in their lungs.

This test is usually combined with a CT scan (PET/CT). Some studies suggest that PET scanning may detect tumors even before they are visible through other studies.

Lung Biopsy

If lung cancer is suspected on imaging studies, the next step is to have a lung biopsy done.

A biopsy relies on a tissue sample that's removed from where the lung cancer is suspected. These cells are then evaluated in a laboratory by a pathologist, who uses a microscope to see if they are cancerous or not. The biopsy also can reveal what type of cancer cells they are.

If lung cancer is diagnosed and spreads, other biopsies may be needed. This is done to evaluate how a cancer is changing over time and to make the most of treatment options as it does.

Removing the tissue for a biopsy can be done through several procedures discussed below.

Bronchoscopy 

In a bronchoscopy, a lung specialist inserts a tube with a lighted scope into the airways to see a tumor. If they see abnormal tissues, the biopsy may be taken during this procedure.

Bronchoscopy is only used in the large upper airways that lead to the lungs, when a tumor there can be reached by using these devices. Patients are given anesthesia to minimize discomfort.

Endobronchial Ultrasound

Endobronchial ultrasound is a relatively new technique used for diagnosing lung cancer.

During a bronchoscopy, healthcare providers use an ultrasound probe within the airway to examine the lungs. They also look at the mediastinum, an area of the body that's between the lungs.

If a tumor is relatively close to the airways, a biopsy can be done by using this technique.

Fine Needle Biopsy

In a fine needle aspiration (FNA) biopsy, a healthcare provider inserts a hollow needle through the chest wall to take a sample of the tumor. A CT is usually done along with this to help the provider find the precise site while doing the biopsy.

This type of biopsy can be done when tumors can't be reached by other techniques. It's especially useful for tumors found near the periphery, or along the outer edges, of the lungs.

Thoracentesis

When lung cancer affects the periphery of the lungs, it can cause fluid to build up between the lungs and the lung lining. This lining is called the pleura, and the space is called the pleural cavity.

Thoracentesis is done by using a large needle to remove a small amount of fluid from this space. This fluid is then tested for cancer cells.

The procedure also can be done to remove a large amount of fluid in people experiencing pain or shortness of breath. In either case, anesthesia is used at the site to keep the person comfortable.

Mediastinoscopy

A mediastinoscopy is done in the operating room under general anesthesia, meaning that a person is fully sedated. A scope is inserted just above the sternum, or breast bone, into the mediastinum in order to take tissue samples from lymph nodes.

These samples can help to determine how far a cancer has spread. This may help your healthcare team to better understand the best possible treatment options.

A PET scan also can be used to look at the mediastinum. It will often provide similar results while avoiding the need for an invasive surgical procedure.

However, the PET scan may not be as effective in detecting cancer in normal-sized lymph nodes. It also cannot be used to provide biopsy tissue samples.

Labs and Tests

During the diagnosis of lung cancer, other tests may be done as well. These are for related reasons but not a part of a diagnosis itself. The tests can include:

• Pulmonary function tests (PFTs): These are used to test lung capacity. They can help to determine how much a tumor interferes with your breathing. They also may be used to see if a specific type of surgery will be safe to do.
• Blood tests: Certain blood tests can detect abnormal changes in chemicals that are made in the body. These changes are caused by lung cancers and can also suggest spread of the tumor.

Sputum Cytology

Sputum cytology involves looking at mucus from the lungs under a microscope. It is the easiest way to confirm a lung cancer diagnosis and type. However, its use is limited to lung cancer cases where the tumors extend into the airways.

Sputum cytology isn't always accurate and it can miss some cancer cells. The test is of most benefit when the result is positive. It is less reliable when the test is negative.

Gene Testing

Gene testing, sometimes called molecular profiling, is often used to understand the changes that occur with specific cancers. These changes, or mutations, won't actually diagnose the cancer.

Rather, they are used to identify specific genes that may be involved. These aren't mutations that you're born with or can pass on. They change as cancer develops and continue to drive its growth.

For example, it's now recommended that people diagnosed with non-small cell lung cancer, and especially the lung adenocarcinoma type, have genetic testing.

This is because treatments that target specific genetic changes may be of benefit.

These targeted therapies are currently approved for people with EGFR mutations, ALK rearrangements, ROS1 rearrangements, and a few other mutations. Other treatments are currently being studied in clinical trials.

Liquid Biopsy

A liquid biopsy is a test done on a sample of blood to look for cancer cells or pieces of tumor DNA.

Most biopsies involve tissue samples, but liquid biopsies allow healthcare providers to monitor some people with lung cancer without invasive procedures.

They can't be used in all cases but are a good example of how the diagnosis and treatment of lung cancer is evolving.

PD-L1 Testing

PD-L1 is a protein that's expressed in greater amounts on some lung cancer cells. This protein serves to enhance the "brakes" of the immune system, reducing its ability to fight off cancer cells.

Some cancer cells manipulate this protein to evade the immune system. Drugs known as checkpoint inhibitors work by blocking this action. They free the immune system to do what it is meant to do.

A PD-L1 test may be done to measure the PD-L1 levels related to your cancer cells. The results may be used to determine if you may benefit from treatment with any of these immunotherapy drugs. However, the understanding of how they work and who might be treated is still limited.

Identifying Type and Stage

Once the tests to confirm a cancer diagnosis are complete, it's important to identify the type and stage of the cancer. This tells you much about how aggressive a cancer might be or how far it has spread. This is essential for your healthcare team to develop the best possible treatment plans.

Non-Small Cell Lung Cancer

Non-small cell lung cancer (NSCLC) is the most common type, accounting for 80% to 85% of lung cancer diagnoses.

Non-small cell lung cancer is further broken down into three types:

• Lung adenocarcinoma is the most common type of lung cancer in the U.S. today, responsible for 40% of all lung cancers. It's the type of lung cancer often found in women, young adults, and in people who don't smoke.
• Squamous cell carcinoma of the lungs tends to occur in or near the large airways—the first place exposed to smoke from a cigarette. Lung adenocarcinomas, in contrast, are usually found deeper in the lungs, where smoke from a filtered cigarette would settle.
• Large cell lung cancer tends to grow in the outer regions of the lungs. These cancers are usually rapidly growing tumors that spread quickly.

There are five stages of non-small cell lung cancer: stage 0 to stage 4.

Small Cell Lung Cancer

Small cell lung cancer (SCLC) accounts for 15% of cases.

It tends to be aggressive and may not be found until it has already spread, especially to the brain. While it usually responds fairly well to chemotherapy, it has a poor prognosis.

Small cell lung cancer is broken down into only two stages: limited stage and extensive stage.

Less Common Types

Other, rarer types of lung cancer include:

• Carcinoid tumors (stages 0 to 4)
• Neuroendocrine tumors (stages 0 to 4)

Determining Spread

Lung cancer most commonly metastasizes, or spreads, to the liver, the adrenal glands, the brain, and the bones.

Common tests used to see if your cancer has spread may include:

• CT scan of the abdomen to check for spread to the liver or adrenal glands
• MRI of the brain to look for spread to the brain
• Bone scan to test for spread to bones, especially the back, hips, and ribs
• PET scan to look for the spread of cancer elsewhere in the body. A PET scan may replace some or all of the other tests listed above.

Differential Diagnoses

Your healthcare provider will consider other possibilities when working to make a diagnosis. Some of the physical symptoms common to lung cancer also might occur with conditions such as:

• Pneumonia, a lung infection that can lead to serious complications
• Tuberculosis, a bacterial infection known for its classic cough symptom
• Bronchitis, an inflammation of the main airways to the lungs
• Pleural effusion, caused by fluid in the space around the lungs
• Pneumothorax, or a collapsed lung
• Chronic obstructive pulmonary disease (COPD), a progressive lung disease linked to smoking

Likewise, the finding of a mass or nodule on imaging could instead be due to:

• Pneumonia
• Fungal or parasitic infections
• Empyema or abscess, a pus-filled infection in the lung
• Benign lung tumor (pulmonary hamartoma) that isn't cancer
• Granuloma, a small area of inflammation, and related infections
• Round atelectasis (partial lung collapse)
• Cysts in the bronchi
• Lymphoma, a cancer that affects the lymphatic system
• Cancer spread from another part of the body

It's common for CT scan results to show lung nodules of an unknown cause. The majority of them prove not to be lung cancer.

Summary

A lung cancer diagnosis is typically made through a series of tests. These tests often begin with a chest X-ray and a physical exam to discuss your symptoms with your healthcare provider.

What's key to know is that the chest X-ray itself cannot diagnose a lung cancer. In fact, many lung cancers are missed on a chest X-ray. So other tests, including the CT, MRI, and PET are used to better evaluate a lung spot or other abnormality.

If needed, a biopsy is then done to confirm a lung cancer diagnosis and what type it is. Other tests are used to stage the cancer and evaluate its spread, and to help develop a treatment plan. As you progress through treatment, some tests may be used to reassess the cancer.

A Word From Verywell

When your tests show a lung spot, shadow, or nodule, it may seem alarming. It's important to follow through to a diagnosis. Even if it is cancer, your chances of survival are better the sooner that you know.