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Home Science Diseases & Conditions Lung Cancer

What Is Lung Cancer?

Lung cancer happens when cells in the lung grow out of control and form a tumor. Lung cancer always starts in the lung. Typically, it takes root in the cells lining the bronchi (the large air passages that lead from the trachea, or windpipe, to the lungs), the bronchioles (small branches of air tubes in the lungs), or alveoli (small air sacs where the lungs and the blood exchange oxygen).1

 

Prevalence of Lung Cancer

Worldwide, lung cancer is the top cause of cancer deaths and the second most diagnosed cancer. In 2019, there were 221,097 new cases of lung cancer in the United States. The disease caused 139,601 deaths that year.2 However, the number of new annual lung cancer diagnoses in the U.S. has been declining. In 2019, there were 52.9 new cases for every 100,000 Americans, a drop from 66.3 new cases a decade earlier.3

Causes and Risk Factors

What Causes Lung Cancer?

Smoking cigarettes is the leading cause of lung cancer, but the disease can occur in people who have never smoked.6,7

The exact causes of lung cancer aren't known, but many factors can increase your risk. The clearest connection is between smoking and lung cancer, with about 80% of lung cancer deaths attributable to smoking and others often attributed to secondhand smoke. Although lung cancer can occur in people who never smoked, it is uncommon.8

Causes of Lung Cancer
Lung Cancer and Genetics

A build-up of genetic changes can lead to lung cancer. This can happen when changes occur in the genes that support cell growth, division, and survival (oncogenes) or in the genes that dictate cell division and death (tumor suppressor genes).8

In non-small cell lung cancer cases, for example, mutations in EGFR or ALK genes often occur in the adenocarcinomas of non-smokers, while KRASmutations are associated with smokers and former smokers.9

Patients typically acquire the genetic changes related to lung cancer during life. Experts have documented lifestyle and environmental factors that increase the risk of genetic mutations, like cigarette smoke and air pollution.7 But the root causes of some changes remain unclear.8

Inherited genetic changes—which come from a person’s parents—can increase the risk of lung cancer,8 but inherited mutations are not associated with many lung cancer cases. Moreover, the increased risk may stem from shared risk factors rather than inherited genetic changes.7

Some lung cancers are linked to acquired genetic changes with abnormalities in DNA.7 The causes of these acquired abnormalities are unclear, but they may be associated with certain risk factors. For example, a mutation in the KRAS gene is present in about 20% to 25% of non–small cell lung cancers (NSCLCs). This gene change enables the cancer cells to grow and spread and can affect the disease and treatment options. Approximately 5% of NSCLCs have a change in the ALK gene, which is more often seen in non-smokers and light smokers. Other examples include NSCLCs that have a rearrangement in the ROS1 gene. seen in 1% to 2% of cases, or changes in the BRAF gene, detected in about 5% of cases.9

 

Lung Cancer Risk Factors

Not everyone who develops lung cancer smokes, and not everyone who smokes develops lung cancer. Lung cancer in nonsmokers and smokers may result from a combination of risk factors.8 Other risk factors for NSCLC, in particular, include:10

  • Asbestos. This material was often used as insulation in buildings, and people may be exposed through their jobs.
  • Radon. Some rocks and soil release this odorless gas.
  • Air pollution. People exposed to outdoor air pollution from factories, cars, fires, and other sources have a higher risk for lung cancer.

 

Lung Cancer Prevention

Not smoking is the best way to avoid lung cancer. Avoiding secondhand smoke is also key to prevention.11

Environmental exposures through work or in the home increase the risk of developing cancer. Wearing a respirator and other protective gear when working with asbestos or other cancer-causing agents can help reduce the risk of developing NSCLC. A radon detector can let you know when high levels of radon are present, and then you can take steps to reduce radon leaks.10

 

Metastatic Lung Cancer

Cancer can spread beyond the original tumor when the tumor sheds cancer cells. These cells enter the bloodstream or lymph nodes, where they can then spread to other parts of the body.12

Cancer is named by the original location of the tumor.12 If lung cancer spreads to another area of the body, it is called metastatic lung cancer.13,14

Lung cancer most often spreads to:13

  • Nearby lymph nodes or other parts of the lung and chest
  • Brain
  • Bones
  • Liver
  • Adrenal glands

Other types of cancer can also spread to the lungs. Those cancers are still named after the original site of the tumor. For example, breast cancer that spreads to the lungs is called metastatic breast cancer.12 Cancers that most commonly spread to the lungs include:14

  • Breast
  • Colorectal
  • Head and neck
  • Kidney
  • Testicular
  • Uterine
  • Lymphoma

Types of Lung Cancer

The two main types of lung cancer are non-small cell (NSCLC) and small cell (SCLC), with NSCLC being more prevalent than SCLC.1

NSCLC is the most common type of lung cancer, accounting for 80% to 85% of all lung cancer cases.1 The two main subtypes of NSCLC are:

  • Adenocarcinoma. The most common subtype, adenocarcinoma forms in the cells that line the outer layers of the lungs, which are responsible for making mucus.4 It is more likely to be caught early before it has spread.1
  • Squamous cell carcinoma. Another common subtype,4 squamous cell carcinoma starts in the flat cells that line the inside airways of the lungs, called squamous cells. This kind of lung cancer is more likely to be associated with smoking.1

SCLC affects about 10% to 15% of people with lung cancer.1 This cancer begins in the nerve cells or hormone-producing cells of the lungs. SCLC tends to spread quickly; for many people, the cancer cells have already spread beyond the lungs by the time they are diagnosed.5

Lung Cancer Symptoms

Signs of Lung Cancer

In some cases, early-stage lung cancer doesn't cause any symptoms, and people don't start to have noticeable symptoms of lung cancer until it has spread.15

Signs to watch for include:15

  • Shortness of breath
  • Coughing up blood
  • Persistent cough
  • Fatigue
  • Chest pain that may get worse with coughing, laughing, or deep breathing
  • Unexplained weight loss
  • Loss of appetite
  • Upper respiratory infections that don't get better
  • Hoarseness
  • Shoulder or back pain
Lung Cancer Symptoms

Lung Cancer Complications

Lung cancer can spread. Signs of metastasis can depend on where in the body the cancer has spread and may include:15

  • Bone pain
  • Dizziness, headache, weakness, numbness of the limbs, seizures
  • Jaundice (yellowing of the skin or eyes)
  • Swelling in the lymph nodes
Lung Cancer Complications
Lung Cancer–Related Syndromes

Lung cancer can sometimes lead to collections of symptoms considered syndromes, including:15

  • Most often associated with NSCLC, Horner syndrome—also called Pancoast tumors—causes eyelid droop, pupil constriction, and other facial symptoms. These are caused by the tumors' effects on the nerves around the eyes and face.

  • Sometimes, tumors can put pressure on a major vein that carries blood to the heart. This causes swelling in the face, neck, arms, or chest. You may also feel dizzy or have headaches.

  • These syndromes are most often associated with SCLC but can occur with any type of lung cancer. Paraneoplastic syndromes occur when hormone-like substances produced by the cancer cells enter the bloodstream. Although the cancer itself hasn't spread, these substances can cause symptoms throughout the body, such as hormone dysfunction, immune system problems, and blood clots. The symptoms from these syndromes are sometimes the first signs of lung cancer, but they aren't always suspected as lung cancer.

Biological Differences in Lung Cancer

The types and number of lung cancer symptoms are similar at diagnosis for all sexes.16 However, the incidence of some lung cancers varies. People assigned female at birth tend to have higher rates of adenocarcinoma and lower rates of squamous cell carcinoma than people assigned male at birth. This may be due to differences between the groups in smoking habits.17

Diagnosis and Treatment

Lung Cancer Diagnosis
  • Screening tests are designed to find illness before symptoms arise. People with lung cancer have a better chance of being treated successfully when the cancer is caught in earlier stages. However, regular chest X-rays as a screening tool for lung cancer haven't proved to help people live longer.18

    Current lung cancer screening guidelines recommend yearly low-dose computed tomography (CT) scans for people who meet all the following three criteria:19

    • Are 50 to 80 years old and in fairly good health
    • Currently smoke or quit smoking within the past 15 years
    • Have a 20 pack-year or more smoking history (a pack-year is the number of packs of cigarettes smoked per day multiplied by the number of years of smoking)
  • Although some lung cancers are found through screening tests, most are found because the cancer has caused symptoms. While screening for cancer, your doctor will perform a physical exam and ask about your history.9

    Different imaging tests can help doctors look for cancer, track its spread, and evaluate a treatment’s progress. A doctor will decide which tests are most appropriate, but some lung cancer tests include:9

    • CT scan
    • Positron emission tomography, or PET scan
    • Magnetic resonance imaging, or MRI scan
    • Bone scan


    To diagnose lung cancer, doctors collect a tissue sample for evaluation.9 This can be done in several ways:

    • Biopsy. A small amount of tissue is removed and examined under a microscope.20, 21
    • Needle biopsy. A hollow needle takes cells or pieces of tissue to be examined under a microscope and undergo molecular testing.9
    • Bronchoscopy. A thin tube is inserted down the throat and into the lungs to look for blockages in the airways. The doctor may remove a tissue sample during this procedure.20, 21
    • Thoracentesis. A small needle is used to collect fluid that may have built up between the lungs and chest wall.20,21


    A doctor may also perform blood tests, tests to see how well your lungs work, and tests to see whether the cancer has spread to the other areas of the chest.9

  • In biomarker testing, particularly for NSCLC, the doctor performs molecular testing of cell or tissue samples to look for abnormalities in DNA or levels of specific proteins such as PD-L1. Finding certain changes in the cancer cells helps guide treatment decisions. It also gives doctors a better understanding of the genetic drivers of the disease and can guide treatment options.20

  • Lung cancer staging is based on the size and location of the tumor and whether the cancer cells have spread beyond the lungs. Based on test results and imaging, your doctor will determine the extent of disease that correlates to a stage.22

    For NSCLC, stages range from stage 0 to stage 4 lung cancer. Higher stages correspond with more extensive disease. The stages of lung cancer are:22

    • Stage 0 lung cancer. The tumor hasn't grown into lung tissue or spread outside the lung.
    • Stage 1 lung cancer. A small tumor hasn't spread to nearby lymph nodes.
    • Stage 2 lung cancer. A larger tumor hasn't spread or a smaller tumor has spread to lymph nodes in the lung.
    • Stage 3 lung cancer. A larger tumor has spread to nearby lymph nodes but not to other parts of the body.
    • Stage 4 lung cancer. The cancer has spread within the chest or to one or more places outside of the chest.


    Doctors tend to stage SCLC using two categories:23

    • Limited stage: The cancer is in one part a patient's chest and potentially treatable with radiation therapy.
    • Extensive stage: The cancer has spread to the other areas of a patient’s body.
Lung Cancer Treatment

People diagnosed with lung cancer have a wide range of treatment options available.24, 25

NSCLC and SCLC have different treatment approaches. Many specialists—including surgeons, oncologists, radiologists, and other healthcare professionals—work together to treat and manage the disease.24, 25

A treatment plan considers the type, stage, and location of the cancer, along with results of biomarker testing, side effects, individual preferences, and your overall health and ability to tolerate treatment. A treatment plan may include a combination of different therapies.24, 25

Surgery aims to remove the tumor completely. It also usually involves removing some lymph nodes in the chest. The surgeon removes some tissue around the tumor for testing to ensure no cancer cells have spread beyond the tumor.24

Surgery is not often used to treat SCLC and is usually reserved for a few cases of limited stage cancer.25 But it has helped treat many patients with stage I and II NSCLC.24 The different types of surgical procedures, particularly for NSCLC, include:24

  • Pneumonectomy. The entire lung is removed.
  • Lobectomy. An entire lobe of the lung is removed. This surgery is the preferred surgical approach when it's possible.
  • Wedge resection. When removing a lobe isn’t possible, the tumor and some surrounding healthy tissue are removed.24 This is often done in individuals who don't have enough lung function to withstand the removal of a full lobe.26


Surgery for lung cancer carries risks similar to any major surgery, including blood clots, infection, and bleeding. Pneumonia is also possible. It can take weeks or months to recover from surgery, depending on the complexity of your procedure.26

Chemotherapy involves intravenous or oral cancer-fighting medications. For NSCLC, chemotherapy can be used before and after surgery, and it’s sometimes used to treat cancer that has spread beyond the lungs.27 It's the most common treatment for SCLC.25

Patients can receive a combination of drugs that work for their specific cancer type. But chemotherapy drugs may kill healthy cells along with cancer cells and have the potential for a range of side effects. Common side effects include fatigue, loss of appetite, hair loss, nausea, vomiting, mouth sores, and higher risk for infection.24, 25

Radiation therapy is commonly used for NSCLC and uses high-energy X-rays or other particles to kill cancer cells. It may be the primary treatment for people who can't undergo surgery. It may also be used before surgery to shrink a tumor, or after surgery to kill any remaining cancer cells.28 In SCLC, it may be used to prevent the spread of cancer cells to other parts of the body, especially the brain.25

This kind of therapy can cause skin irritation, nausea, vomiting, loss of appetite, and sometimes, hair loss where the radiation beam contacts the skin. Most side effects go away when treatment stops.28

Immunotherapy is a growing area of treatment for lung cancer that uses the body's own immune system to fight cancer. These treatments target certain immune system pathways to help the immune system slow or stop the growth of cancer cells.24, 25

Immunotherapies are available to treat NSCLC and SCLC either alone or in combination with other therapies, including chemotherapy. The choice of treatment depends on many factors, including your type of cancer, stage, and health.24,25

These treatments are associated with side effects, such as fatigue, nausea, itching, and diarrhea. Other side effects related to the medication's effects on the immune system are possible.29, 30

Targeted therapies are medications that work to directly target genetic mutations, proteins, or other molecular aspects of the tumor that cause the cancer to grow. These therapies are chosen based on biomarker or molecular testing of tumor samples to understand the characteristics of the cancer.24 Targeted therapies currently available for NSCLC include:31

  • Monoclonal antibodies
  • Tyrosine kinase inhibitors
  • Mammalian target of rapamycin inhibitors
Living With Lung Cancer

Getting a cancer diagnosis brings about a lot of emotions.32

Each type of treatment has a different recovery journey, and some have long-term side effects.32

Maintaining a healthy lifestyle, with moderate physical activity and healthy foods, can help overall health. If you haven't quit smoking, quitting now may still benefit you.32

You may consider support from family, friends, and professionals or support groups. Many resources are available to answer questions or connect you to supportive care.32

Lung Cancer Prognosis

The outlook and survival time for lung cancer vary by stage, type of cancer, and molecular characteristics of the cancer, as well as by patient age and overall health, along with many other factors. 

Relative survival rates offer some insight into the outlook for specific types and stages of cancer by comparing the survival rates of people who have a disease with the survival rates of the general population. If a lung cancer patient’s five-year relative survival rate at diagnosis is 60%, the patient is 60% as likely to live five years as people who do not have the disease.34

Newer treatment options steadily improve the approach to lung cancer treatment and the lung cancer survival rates.33

Five-year survival rates for NSCLC are estimated to be:33

  • Overall: 26%
  • Localized disease, showing no sign that the cancer has spread outside the lung: 64%
  • Regional disease, in which the cancer has spread to structures or lymph nodes outside the lung: 37%
  • Distant disease, in which the cancer has spread to distant parts of the body: 8%

For SCLC, five-year survival rates are:33

  • Overall: 7%
  • Localized disease: 29%
  • Regional disease: 18%
  • Distant disease: 3%

Global Impact of Lung Cancer

Global Impact of Lung Cancer

As the second most common cancer in the world, lung cancer diagnoses reached 2.21 million new cases in 2020. It is the leading cause of cancer death worldwide.34 Tobacco is a leading risk factor of lung cancer, linked to about 75% of lung cancer deaths in people assigned male at birth and 50% in people assigned female at birth globally.35

The global annual cost of cancer, including direct healthcare costs and disability, totals hundreds of billions of dollars and is expected to increase.35 In the United States, lung cancer costs an estimated $13.4 billion in healthcare costs and $36.1 billion in productivity losses due to early death from lung cancer.36

The United States and many countries in Europe experienced a tobacco epidemic early and have since seen declines in smoking and lung cancer. Other countries that experienced tobacco epidemics later are still experiencing increasing lung cancer rates.35

Frequently Asked Questions About Lung Cancer

  • The overall five-year relative survival rate for NSCLC of all stages is 26%. The overall five-year relative survival rate for SCLC is 7%. However, these numbers do not fully reflect the advances made in lung cancer treatment within the past decade. Survival varies by type of disease, the molecular characteristics of the disease, age, overall health, and other factors.33

  • Cigarette smoking is the main risk factor for lung cancer. Smokers are 15 to 30 times more likely than nonsmokers to develop lung cancer or die from lung cancer. Quitting smoking immediately starts to lower your risk for developing cancer.37

  • For most people, available treatments do not cure NSCLC31 or SCLC.38 But for some early-stage NSCLC, surgery may effectively offer a cure.25

  • People with a family history of lung cancer tend to be at slightly higher risk for developing the disease, but most lung cancers are not caused by inherited genetic changes and may be based on certain shared risk factors.7

    Some lung cancers have acquired genetic changes with certain abnormalities in DNA that are acquired and not inherited.8 The cause of these acquired abnormalities are unclear and may be associated with certain risk factors. For example, a mutation in the KRAS gene is present in about 20% to 25% of non–small cell lung cancers (NSCLCs). This gene change enables the cancer cells to grow and spread. These gene changes have been found to affect the disease and treatment options.9

    About 5% of NSCLCs have a change in the ALK gene, which is more often seen in non-smokers and light smokers. Other examples include NSCLCs that have a rearrangement in the ROS1 gene, seen in 1% to 2% of cases, or changes in the BRAF gene, detected in about 5% of cases.9

Learn More About Lung Cancer

Find Pfizer clinical trials for lung cancer at PfizerClinicalTrials.com.

Explore lung cancer clinical trials at ClinicalTrials.gov.

Area of Focus: Oncology

Lung Cancer is a focus of Pfizer’s Oncology Therapeutic Area. Visit the Oncology Page.

The information contained on this page is provided for your general information only. It is not intended as a substitute for seeking medical advice from a healthcare provider. Pfizer is not in the business of providing medical advice and does not engage in the practice of medicine. Pfizer under no circumstances recommends particular treatments for specific individuals and in all cases recommends consulting a physician or healthcare center before pursuing any course of treatment.

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