• Also Known As:
  • Non-Small Cell Lung Cancer
  • Small Cell Lung Cancer
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What is lung cancer?

Lung cancer is the uncontrolled growth of abnormal cells originating within the lungs, usually in the layers of cells that line the air passages. These abnormal cells do not go through the natural stages of growth, division, and dying that normal cells do. They replicate unchecked, often forming one or more masses of cells (tumors). Tumors can damage healthy tissue and grow large enough to interfere with breathing. Lung cancer can eventually spread (metastasize) beyond the lungs into nearby lymph nodes, tissues, and other organs.

The lungs are part of the respiratory (breathing) system and are located in the chest, inside the rib cage and above the diaphragm. When a person inhales, air enters the lungs and flows through passages of decreasing diameter called bronchi and bronchioles. These passages carry oxygen to small sacs (alveoli) deep within the lung, where oxygen moves from the lung into the bloodstream, and carbon dioxide, a byproduct of metabolism, moves from the blood into the lung to be exhaled. Any lung disease that interferes with this exchange process, including lung cancer, can limit the amount of oxygen available and affect tissues and organs throughout the body.

According to the American Cancer Society (ACS), lung cancer is the second most common cancer in both men and women (other than skin cancer) and it is the leading cause of cancer death worldwide. More people die of lung cancer each year than of breast, prostate, and colon cancer combined. Globally, about 13% of all new cancers are lung cancers. In the U.S., the ACS estimates there are about 230,000 new cases of lung cancer each year and about 150,000 people die of the disease. While anyone can get lung cancer, most new cases will be in people 65 years of age or older. The average age at the time of diagnosis is about 70.

Lung cancer begins in one of the cell types that exist in the lungs. Most cases are thought to be due to acquired genetic changes or mutations in DNA that either promote the uncontrolled growth of cells or inhibit their natural death.

The lungs are also a common site for metastasis from other cancers, such as breast cancer and liver cancer. Cancer that spreads from another part of the body to the lungs, such as metastatic breast cancer, is not considered lung cancer. Cancers that have spread to the lungs from other areas are treated differently so they are not covered in this article.


About Lung Cancer

Risk Factors

Risk factors for developing lung cancer include:

  • Smoking – More than 87% of lung cancer deaths are thought to be related to smoking. The more a person smokes, and the longer that he or she smokes, the greater the risk. Second-hand smoke also increases risk of lung cancer.
  • Radon exposure – A common cause of lung cancer in nonsmokers, radon is a colorless, odorless radioactive gas that occurs naturally in soil but can accumulate in some homes.
  • Asbestos exposure – This can increase the risk of lung cancer. Asbestos is more commonly associated with mesothelioma, a rare cancer of the lining of the chest and abdomen. Most cases of mesothelioma – about 70% to 80% – arise in people with a history of working with asbestos, especially in the shipbuilding, construction, automotive, and fireproofing industries.
  • Exposure to cancer-causing substances (carcinogens) such as arsenic, cadmium, or chromium (often in the workplace)
  • Air pollution, especially near heavily trafficked roads
  • Radiation therapy, such as previous treatment for another type of cancer
  • Family or personal history of lung cancer
  • HIV or tuberculosis infection
  • Long-term pulmonary fibrosis


There are two main categories of lung cancer, non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). These cancers are named and differentiated based upon the size, shape, and characteristics of the tumor cells. In addition, there are several less common types of cancer that can affect the lungs.

The following table lists the different types of lung cancers.

Type of Lung Cancer Percentage of Lung Cancers Comments
Non-small cell lung cancer (NSCLC) 80-85% Most cases of lung cancer are in this category.
  • Squamous cell carcinoma
25-30% Squamous cells are flat cells that are normally found in the skin, mouth, and throat but not the lungs. They develop in the lungs in response to ongoing injury; this type of lung cancer is primarily seen in smokers.
  • Adenocarcinoma
40% This cancer originates in the cells that secrete mucus and mainly seen in current or former smokers but is also the most common type seen in non-smokers.
  • Large cell (undifferentiated) carcinoma
10-15% This type tends to grow and spread quickly. It also occurs mainly in smokers.
  • Various subtypes
Much less common Examples include adenosquamous carcinoma and sarcomatoid carcinoma.
Small cell lung cancer (SCLC) 10-15% Also known as oat cell cancer and small-cell undifferentiated carcinoma; this type is primarily seen in smokers.
Lung carcinoid tumors Rare Most often are slow-growing
Mesothelioma Rare Cancer of the lining of body cavities, including the chest and abdomen; people can develop mesothelioma 20 to 50 years after asbestos exposure.
Other tumors found in the lungs Rare Examples include sarcomas and lymphomas.

Signs and Symptoms

It is difficult to detect lung cancer at an early stage. There are often no symptoms until the condition is advanced. Examples of symptoms include:

  • Persistent cough
  • Persistent or recurrent lung infections (for example, pneumonia or bronchitis)
  • Hoarseness
  • Shortness of breath
  • Wheezing
  • Pain when swallowing
  • Chest pain
  • Fatigue or weakness
  • Weight loss
  • Loss of muscle mass
  • Loss of appetite
  • Coughing up blood

When lung cancer spreads to other areas of the body (metastasizes), other signs and symptoms related to those sites may develop. Examples include bone pain, neurological symptoms (headache, drooping of eyelids, and changes in gait or the way you walk), jaundice (yellowing of the skin and eyes), swollen lymph nodes (neck or facial swelling), and blood clots or bleeding tendency.


The goals with testing for lung cancer are to detect it as soon as possible, determine the specific type and how far it has spread, help guide treatment, and evaluate a person’s general state of health and lung function.

There are no blood tests that can be used to screen for or detect lung cancer. However, recent guidelines from the American College of Chest Physicians, American Cancer Society, the U.S. Preventive Services Task Force, and National Comprehensive Cancer Network recommend that people who have a significant risk of developing lung cancer due to age and previous or current smoking history be offered periodic low-dose computed tomography (LDCT) scanning to help detect early lung cancer. This recommendation is limited to those at a significant risk, and screening should only be done by facilities that are experienced with the procedure. For information on this type of procedure, visit RadiologyInfo.org: Computed tomography, chest.

Sometimes a chest X-ray may be used to observe the lungs and nearby structures to look for tumors. Likewise, sputum cytology, a method of obtaining cells from the lungs, may be used to look for cancer cells. However, these procedures are not recommended for screening purposes by any established guidelines.

Diagnosis and Staging
A diagnosis of lung cancer is usually confirmed by examining tissue and/or cells from the lungs with a microscope. If the tissue or cells are cancerous, the next step is to determine the stage (or extent) of disease. The stage is categorized by how far the lung cancer has spread from its original site. Staging may involve evaluations, such as a physical exam or imaging tests, that look for evidence of cancer in other organs or parts of the body. Treatment will depend in part on the stage of the cancer.

Laboratory tests used for diagnosis and staging include:

  • Biopsy – when a suspected cancer is found, some tissue from the suspicious site is removed for examination under a microscope by a pathologist. Often, a long, thin, lighted tube called a bronchoscope is inserted into the airways to view the structures and collect a tissue sample. In some cases, a sample of tissue may be collected during a surgical procedure. The way the tissue is obtained is often based on where in the lung the suspected cancer is located. These samples can be tested for genetic mutations or presence of specific targets for targeted therapy and immunotherapy.
  • Cytology – this procedure may be used to help establish a diagnosis of lung cancer by examining cells. A sample of cells may be collected by inserting a small needle into the lungs and aspirating the cells (sometimes called a needle biopsy, fine needle aspiration, or FNA). Also, cells can be examined from a sample of fluid collected during a bronchoscope examination or in a sample of sputum. Sputum samples (deep respiratory secretions, not saliva) may be coughed up and expelled into a sterile cup provided by the laboratory. If a person cannot produce a sputum sample, then it can often be induced by inhaling a sterile saline or glycerin aerosol for several minutes to loosen phlegm in the lungs.
  • Pleural fluid analysis – this is an evaluation of fluid removed from the space between the lungs and chest wall by a procedure called thoracentesis. It may be used as part of staging to help determine whether cancer has spread to the outside lining of the lungs. This is only done in people who have an increased amount of fluid in this space since normally the amount of fluid present is too small to sample safely.

Tests for Targeted Therapy
Tests may be performed on tumor tissue or cells to help guide therapy. Some people with non-small cell lung cancer (NSCLC) may be candidates for targeted therapy, depending on the type of NSCLC and results of some molecular tests. Targeted therapy is a newer type of cancer treatment that uses drugs that have a greater effect on cancerous tissue, reducing many of the side effects associated with standard therapy. It is based on the fact that the genetic makeup of the cancer cells is different than the normal cells around them. Targeted therapy aims to disrupt specific steps or processes that are somewhat unique to the growth of cancer cells.

Testing for targeted therapy may include:

  • EGFR (epidermal growth factor receptor) gene mutation – present in 10% to 15% of adenocarcinoma NSCLCs; if present, a person is more likely to respond to tyrosine kinase inhibitor drug therapies such as gefitinib and erlotinib.
  • KRAS gene mutation – present in 20% to 30% of adenocarcinoma NSCLCs; if present, a person is less likely to respond to tyrosine kinase inhibitors.
  • ALK gene mutation / gene rearrangement (EML4-ALK, about 5% of NSCLCs) – most often seen in light smokers or non-smokers with adenocarcinoma. If a mutation is present, the cancer is more likely to respond to ALK inhibitors such as crizotinib and less likely to respond to other tyrosine kinase inhibitors.
  • ROS1 gene mutation (1% to 2% of adenocarcinoma NSCLCs) – those with ROS1 gene rearrangements are more likely to respond to crizotinib and less likely to respond to other tyrosine kinase inhibitors.
  • PD-L1 – another form of targeted therapy is the immunotherapy “immune checkpoint inhibition” (see Treatment below), which requires tumors to possess a certain level of PD-L1 protein on its surface to be targeted by therapy. Therefore, tissue from a tumor may be tested for PD-L1 to determine if the patient is a good candidate for immunotherapy.

Other laboratory tests
General testing is often used to help assess an affected person’s health and/or to monitor them during treatment. Some of these tests may include:

Non-laboratory tests
Pulmonary function tests (PFTs) may be used to help evaluate lung function. For more complete information, visit the web site for Johns Hopkins Medicine: Pulmonary Function Laboratory.

A variety of imaging tests are used to help diagnose and stage lung cancers. They include:

  • Chest X-ray
  • Computed tomography (CT) scan
  • Magnetic resonance imaging (MRI) scan
  • Positron emission tomography (PET) scan
  • Ultrasound
  • Bone scan

For additional details about these procedures, visit RadiologyInfo.org.


Appropriate lung cancer treatment depends upon the type of cancer, its stage, and its characteristics. Staging evaluates the size of the cancer, its location, and how far it has spread. Treatments may include:

  • Surgery to remove part of a lobe of a lung, a lobe of a lung, or an entire lung if the tumor is still localized and in its early stage
  • Surgery to help relieve symptoms such as airway blockages or fluid buildup
  • Radiation therapy, alone or in combination with surgery
  • Chemotherapy as a single therapy or in combination with targeted therapy or radiotherapy; it can also be complementary to surgery.
  • Radiosurgery is an intense radiation treatment for people with small lung cancers who can’t undergo surgery.
  • Targeted drug therapy
    • Drugs that target tumor blood vessel growth (angiogenesis)
    • Drugs that target EGFR – tyrosine kinase inhibitor drug therapies
    • Drugs that target the protein made by an altered ALK gene
  • Immunotherapy has recently emerged as a cancer therapy. Immunotherapy is designed to boost the body’s natural immune system to fight the cancer. It targets molecules called “immune checkpoints” such as PD-1 and PD-L1, which serve as brakes to stop immune system over-activation so the immune system doesn’t attack “self” tissue. Cancer cells are able to use these immune checkpoints to lessen the immune response against them. This may allow cancer cells to escape the immune attack and survive. Blocking this pathway with PD-1 and PD-L1 antibodies has stopped or slowed the growth of lung cancer for some patients.

People who become resistant to available treatments and/or have inoperable lung cancer may want to consider enrollment in clinical trials of new treatments. There are promising areas of research that may offer them additional options. For more on this, see Clinicaltrials.gov. For additional details on treatment, see the links under Related Content.

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