Lung cancer starts when cells in the lungs grow abnormally and form tumors

Lung cancer occurs when cells in the lungs begin to divide uncontrollably, creating a mass of abnormal tissue. Unlike normal lung cells, which grow, divide, and die in an orderly way, cancer cells ignore the body's signals to stop dividing. Over time, these cells can spread to other parts of the lungs or to distant organs.

The lungs are two spongy organs in your chest that take in oxygen when you breathe and release carbon dioxide when you exhale. Cancer can start in the cells that line the airways (bronchi), in the small air sacs at the end of the airways (alveoli), or in other lung tissue. Most lung cancers begin in the cells lining the airways.

Not all lung tumors are cancer. Some are benign (non-cancerous) and do not spread. A doctor can determine whether a tumor is cancerous by examining cells under a microscope or using other tests.

Key Takeaways

  • Lung cancer develops when cells in the lungs grow abnormally and form tumors that can spread to other parts of the body.
  • The two main types are non-small cell lung cancer (about 85% of cases) and small cell lung cancer (about 15% of cases), named for how the cells look under a microscope.
  • Smoking is the leading cause, but lung cancer also occurs in people who have never smoked, often linked to radon, secondhand smoke, or family history.
  • Early-stage lung cancer often causes no symptoms, which is why screening with low-dose CT scans is recommended for people at high risk.
  • Doctors determine how far cancer has spread using a staging system that ranges from stage 1 (localized) to stage 4 (spread to distant organs).

The two main types of lung cancer

Non-small cell lung cancer (NSCLC) accounts for roughly 85% of all lung cancer cases. It grows more slowly than small cell lung cancer and is more likely to be caught before it spreads widely. NSCLC has three subtypes: adenocarcinoma (which starts in mucus-producing cells and is the most common type overall), squamous cell carcinoma (which starts in flat cells lining the airways), and large cell carcinoma (a less common form).

Small cell lung cancer (SCLC) makes up about 15% of cases. It grows quickly and spreads to other organs earlier than NSCLC. SCLC is strongly linked to smoking and is less common in people who have never smoked.

The distinction matters because the two types respond differently to treatment. A pathologist examines cancer cells under a microscope to determine which type is present, and this finding shapes the treatment plan a doctor recommends.

What causes lung cancer to develop

Smoking is the leading cause of lung cancer, accounting for about 80% of cases. When you inhale tobacco smoke, harmful chemicals enter the lungs and damage the cells lining the airways. Over years or decades, this repeated damage can cause cells to become cancerous.

Lung cancer also occurs in people who have never smoked. Radon, a naturally occurring radioactive gas that seeps into buildings from soil, is the second leading cause of lung cancer overall and the leading cause among non-smokers. Radon accumulates in basements and lower levels of homes and buildings, and long-term exposure increases risk. Secondhand smoke exposure also raises the risk of lung cancer in non-smokers. Other risk factors include a family history of lung cancer, previous lung disease such as chronic obstructive pulmonary disease (COPD), and occupational exposure to asbestos or other carcinogens.

Lung cancer can develop at any age, but it is most common in people over 65. The disease typically takes years to develop, which is why it is rare in younger people unless there is a strong family history or significant exposure to a carcinogen.

How lung cancer spreads and is staged

Cancer cells can spread (metastasize) through the lymph system or the bloodstream. From the lungs, cancer cells may travel to nearby lymph nodes, then to the chest wall, heart, or other organs. Common sites of spread include the brain, bones, liver, and adrenal glands.

Doctors use a staging system to describe how far cancer has spread. Stage 1 means the cancer is localized to the lung and has not reached nearby lymph nodes. Stage 2 indicates the cancer has spread to nearby lymph nodes or is larger. Stage 3 means the cancer has spread to lymph nodes in the center of the chest or to the chest wall. Stage 4 means the cancer has spread to distant organs or to both lungs.

Staging is determined through imaging tests such as CT scans, PET scans, and sometimes MRI or brain imaging. A biopsy—removal of a small tissue sample for examination—confirms the diagnosis and provides information about the cancer's characteristics. Staging guides treatment decisions and helps doctors estimate prognosis.

Symptoms and how lung cancer is detected

Early-stage lung cancer often produces no symptoms, which is why it may not be detected until the disease is more advanced. When symptoms do appear, they may include a persistent cough lasting more than three weeks, coughing up blood, chest pain that worsens with breathing or coughing, hoarseness, shortness of breath, or recurring pneumonia.

Symptoms depend on the cancer's location and size. A tumor in the center of the lungs may not cause symptoms until it is large, while a tumor near the edge of the lung may irritate the pleura (the lining around the lungs) and cause chest pain earlier.

Lung cancer is sometimes found by accident on imaging done for another reason, such as a chest X-ray for an injury or infection. In people at high risk—such as current or former heavy smokers—low-dose CT screening can detect cancer at an earlier stage when treatment is more effective. A doctor can discuss whether screening is appropriate based on age, smoking history, and other risk factors.

How doctors diagnose lung cancer

If imaging suggests a possible lung tumor, a doctor must obtain a tissue sample to confirm the diagnosis. This is done through a biopsy, which can be performed in several ways. A bronchoscopy allows a doctor to pass a thin tube down the airway to reach tumors in the central lungs. A needle biopsy uses imaging to guide a needle through the chest wall to reach a tumor in the outer lung. A thoracentesis removes fluid around the lungs if cancer has spread to the pleura.

Once a biopsy confirms lung cancer, additional tests determine the cancer's type and characteristics. Molecular testing examines the cancer cells for specific mutations or genetic changes that may affect treatment options. For example, some non-small cell lung cancers have mutations in the EGFR gene or ALK gene, which can be targeted with specific drugs.

Imaging tests such as CT, PET, and MRI determine the cancer's stage by showing whether it has spread to lymph nodes or distant organs. A brain MRI is often done because lung cancer frequently spreads to the brain.

Treatment approaches depend on type and stage

Treatment options for lung cancer include surgery, radiation therapy, chemotherapy, targeted therapy, and immunotherapy. The choice depends on the cancer's type, stage, location, and the patient's overall health.

Surgery removes the tumor and surrounding tissue and is most effective for early-stage cancers that have not spread widely. A surgeon may remove a small section of lung (wedge resection), a lobe (lobectomy), or an entire lung (pneumonectomy).

Radiation therapy uses high-energy beams to kill cancer cells. It may be used alone for early-stage cancers or combined with chemotherapy for more advanced disease. Chemotherapy uses drugs that circulate through the bloodstream to kill cancer cells throughout the body and is often used for advanced-stage lung cancer.

Targeted therapy and immunotherapy are newer approaches that work differently than traditional chemotherapy. Targeted drugs attack specific mutations in cancer cells, while immunotherapy drugs help the immune system recognize and destroy cancer cells. These treatments are increasingly used for advanced non-small cell lung cancer and have improved survival rates for many patients.

Frequently Asked Questions

Can you get lung cancer if you have never smoked?

Yes. Radon exposure is the leading cause of lung cancer in non-smokers, followed by secondhand smoke, family history, and occupational exposures. About 10% to 15% of lung cancer cases occur in people who have never smoked.

What is the difference between a lung nodule and lung cancer?

A nodule is a small spot on imaging that may or may not be cancer. Many nodules are benign and do not grow. Doctors monitor nodules over time with follow-up imaging to see if they change in size or appearance, which would suggest cancer.

Does lung cancer always spread to other organs?

Not always. Early-stage lung cancer that is caught and treated before it spreads may not metastasize. However, lung cancer has a tendency to spread, which is why staging and treatment are based partly on the risk of spread.

How long does it take for lung cancer to develop?

Lung cancer typically develops over years or decades of exposure to a carcinogen such as tobacco smoke or radon. The exact timeline varies widely depending on the cause, the individual's genetics, and other factors.

What is the survival rate for lung cancer?

Survival rates vary significantly by stage at diagnosis and cancer type. Early-stage cancers have higher survival rates than advanced-stage cancers. Advances in targeted therapy and immunotherapy have improved outcomes for many patients in recent years.