What Is Lung Cancer?

Lung cancer occurs when malignant (cancerous) cells within the lungs—often the bronchi, bronchioles or alveoli—grow and multiply out of control, with the abnormal cells forming a tumor. Lung cancer is the leading cause of death from cancer worldwide. Lung cancer may start in the lungs but can spread to lymph nodes and other organs, such as the brain.

What Are the Types of Lung Cancer?

The two main types of lung cancer are small cell lung cancer and non-small cell lung cancer, named for how large the cancer cells appear when viewed under a microscope. Roughly 85% of all lung cancers are non-small cell lung cancer (NSCLC). Small cell lung cancer (SCLC) has a much lower rate of occurrence.

  • Non-small cell lung cancer (NSCLC): Multiple types of NSCLC occur, but adenocarcinoma is most common. Other types of NSCLC, which can spread quickly, include squamous cell carcinoma, which starts in the squamous cells near the central part of the lung, and large cell carcinoma. Rarer versions include adenosquamous carcinoma and sarcomatoid carcinoma
  • Small cell lung cancer (SCLC): An even faster spreading type of lung cancer than NSCLC, small cell lung cancer is often spreading by the time a diagnosis is made and is almost always caused by smoking

How Common Is Lung Cancer?

The World Health Organization estimates that more than 2.21 million new cases of lung cancer are diagnosed each year worldwide, making it the second-most common cancer behind breast cancer. Continued research into lung cancer has improved the medical community's understanding of the disease, and lung cancer treatments continue to advance. However, lung cancer is still the leading cause of death from cancer worldwide.

What Are the Causes and Risk Factors of Lung Cancer?

The leading cause of lung cancer is linked to smoking. While non-smokers can still be diagnosed with lung cancer—as many as 25% of all lung cancer patients never smoked—the carcinogens in smoking damage the cells lining the lung immediately. The body will start a repair process, but for every exposure to smoking's chemicals, the cells are further damaged and eventually may lead to cancer.

Lung cancer risk factors include:

  • Smoking: The risk of lung cancer greatly increases every time a patient smokes and heightens the chance that other risk factors become more dangerous
  • Secondhand smoke exposure: The chemicals in the smoke can still damage lung cells, even with secondhand smoke
  • Radon gas exposure: Radon can be present in buildings and the gas can damage lung cells
  • Carcinogen exposure: Whether asbestos, arsenic, chromium or other known carcinogens, exposure to these chemicals can increase your risk for lung cancer
  • Radiation therapy: Often used to treat cancer, exposure to radiation increases the risk of developing a new cancer
  • Family history: Those with a close family member with lung cancer have increased odds of a lung cancer diagnosis

What Are the Symptoms of Lung Cancer?

Lung cancer symptoms may not always appear unique to lung cancer and can often resemble other health problems. Rarely will early symptoms appear. It isn't until the appearance of advanced lung cancer symptoms that patients notice a change. Visiting your doctor at the first signs or symptoms of lung cancer can help lead to an earlier diagnosis. The most common early signs of lung cancer include:

  • A new cough that won't fade
  • A cough with phlegm or sputum
  • Hoarseness when speaking
  • Weakness or wheezing
  • Recurring infections
  • Chest pain that intensifies with coughing

More advanced lung cancer symptoms could also include:

  • Bone pain
  • Headaches
  • Muscle weakness or eyelid drooping
  • Unintentional weight loss

Signs and symptoms of lung cancer don't differ much between small cell lung cancer and non-small cell lung cancer, except in cases of Pancoast tumors, which appear in the upper part of the lung and usually result from non-small cell lung cancer. Symptoms for these types of tumors can include severe shoulder pain, drooping eyelid on one side of the face and a smaller pupil in the same eye.

How Is Lung Cancer Diagnosed?

The first step in a lung cancer diagnosis is to complete a medical history and physical exam. To diagnose lung cancer, your doctor may also order diagnostic tests for lung cancer and procedures such as:

  • X-rays: These images can show any mass or spot on the lungs that might be cancer
  • Computed tomography (CT) scan: A series of X-ray images of inside the body are combined to produce cross-sectional views of the lung. This test can show a tumor along with its spread elsewhere in the body
  • Positron Emission Tomography (PET) scan: A PET scan uses a special dye that allows doctors to see how the body tissues are working and what they look like. This test can show whether a tumor has spread elsewhere in the body
  • Magnetic Resonance Imaging (MRI) scan: An MRI scan uses strong magnetic fields and radio waves to capture detailed images of organs and tissues in the body. MRIs are very useful for imaging the brain and spinal cord
  • Biopsy: A small sample of tissue or fluid is removed from the lung. A pathologist then views it under a microscope to check for cancer. Biopsies are vital for obtain cancerous tissue for genetic testing. A biopsy may be done by methods such as:
    • Fine needle aspiration biopsy: A thin, hollow needle is used to remove tissue or fluid from the lung
    • Thoracentesis: A hollow needle is inserted into the chest wall to remove fluid
    • Bronchoscopy: A flexible tube called a bronchoscope is passed down through the nose or mouth and into the bronchi to remove tissue
    • Mediastinoscopy and thoracoscopy: With both of these procedures, a thin, tube-shaped instrument is inserted into the chest to obtain tissue or lymph node samples

Lung Cancer Screening

Lung cancer screening improves the ability to detect lung cancer at an early stage, when it has the best chance to respond to treatment. Mass General uses low-dose CT scans to screen lung cancer among high-risk individuals. Learn more about Mass General's lung cancer screening.

Staging Lung Cancer

Tests and procedures can also help your doctor determine the stage of lung cancer. Staging is a way of describing how much the cancer has grown, how big it is and whether it has spread to other parts of the body. Staging is important because it helps your doctor plan your treatment and determine your outlook (prognosis). Lung cancer has 4 stages, numbered from 1 to 4.

  • Stage 1 means that the cancer is relatively small and contained within the lung
  • Stages 2 and 3 mean that the cancer is larger than stages 1 and 2 and may have spread into lymph nodes and surrounding tissues close to the tumor
  • Stage 4 means that the cancer has spread to the lung lining, the opposite lung, or another body organ. This is also called metastatic cancer

Learn about the stages of non-small cell lung cancer and the stages of small cell lung cancer on the National Cancer Institute website.

Treating Lung Cancer

If you are diagnosed with lung cancer, your care team will work with you to develop a treatment plan that is right for you. This plan will depend on the type and stage of your cancer, your general health and your treatment preferences.

Lung Surgery

Lung cancer surgery may involve removal of a tumor and some nearby healthy tissue, part of a bronchus, an entire lobe (section) of a lung or an entire lung. Chemotherapy or radiation therapy may also be used to kill any cancer cells left behind. Common lung surgery procedures include:

  • Sleeve resection: Part of a bronchus, the main airways of the lungs
  • Wedge resection: A tumor and some nearby healthy tissue
  • Lobectomy: An entire section of a lung
  • Pneumonectomy: An entire lung

Non-Surgical Lung Cancer Treatments

Other common treatment options for lung cancer include the following:

  • Immunotherapy helps your immune system fight cancer. The immune system helps your body fight infections and other diseases. It is made up of white blood cells and organs and tissues that are part of the lymph system. Some types of immunotherapies are also sometimes called biologic therapy or biotherapy
  • Chemotherapy kills cancer cells using intravenous (IV) or oral drugs
  • Targeted therapy uses drugs that attack specific parts of cancer cells, depending on if you have a genetic mutation and what type of mutation it is. These drugs work differently from standard chemotherapy drugs
  • Radiation therapy uses high-energy radiation beams to kill or shrink a tumor while sparing healthy tissue. The radiation source can come from outside the body (external radiation therapy) or from implants inside the body (internal radiation therapy)
  • Thermal ablation uses needles introduced through the skin to kill a tumor while sparing healthy tissue
  • Clinical trials may provide access to new and promising therapies for lung cancer

Lung Cancer Prevention

The best lung cancer prevention strategy is to stop smoking. Eliminating other risk factors, such as exposure to secondhand smoke or other carcinogenic chemicals, can help prevent lung cancer. Removing smoking from your lifestyle is the best preventative measure. Learn more about Mass General's Smoking Cessation Programs to get you started.

Lung Cancer FAQs

Mass General has put together a list of answers to common questions about lung cancer. For additional questions and information, visit our lung cancer FAQs page.

How Does Smoking Cause Lung Cancer?

The carcinogens contained in cigarette smoke immediately damage the cells lining the lung. The body will start a repair process, but for every exposure to a cigarette's chemicals, the cells are further damaged. Eventually, they may lead to the development of abnormal cells that turn cancerous. The risk of lung cancer increases with every exposure to smoking's carcinogens.

What Is the Second Leading Cause of Lung Cancer?

The naturally occurring radioactive gas radon is the second-leading cause of lung cancer. This inert, colorless and odorless gas appears naturally in the atmosphere and disperses quickly, typically without any health risks. But radon gas can get trapped indoors, increasing the risk of the gas entering the lungs.

How Serious Is Lung Cancer?

The second-most diagnosed form of cancer worldwide every year, lung cancer is the leading cause of death from cancer across the globe. Roughly 150,000 Americans die from lung cancer each year and, on average, the American Cancer Society says that patients diagnosed with lung cancer have a 60% survival rate over five years.

What Are the Four Types of Lung Cancer?

The four most common types of lung cancer are non-small cell lung cancer, small cell lung cancer, lung nodules and mesothelioma, a rare cancer of the chest lining.

What Is Advanced Lung Cancer?

When cancer spreads, it is known as metastatic cancer. Advanced lung cancer occurs when cancer has spread from the lungs to other organs or when cancerous fluid collects around the lung. Advanced lung cancer symptoms often include an increase in typical lung cancer symptoms and could extend to signs and symptoms of cancer in other parts of the body.