Lung Cancer Basics | American Lung Association

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Lung Cancer Basics

Lung cancer is a complex disease to understand and treat. Get the basics on how lung cancer starts, different types, how it affects your body and other information you need to know.

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Key Points

  1. Lung cancer happens when cells in the lung change (mutate). They grow uncontrollably and cluster together to form a tumor.
  2. Lung cells most often change because they are exposed to dangerous chemicals that we breathe.
  3. There are two main types of lung cancer, small cell lung cancer and non-small cell lung cancer. Non-small cell lung cancer is more common.
  4. Lung cancer symptoms usually do not appear until the cancer has spread to other parts of the body. At this point, it is harder to treat lung cancer.

What Is Lung Cancer?

Lung cancer is cancer that starts in the lungs. When a person has lung cancer, they have abnormal cells that cluster together to form a tumor. Unlike normal cells, cancer cells grow without order or control, destroying the healthy lung tissue around them. These types of tumors are called malignant tumors. When the cancer cells spread, they prevent organs of the body from functioning properly.

Why Are Malignant Tumors Dangerous?

One reason malignant tumors are dangerous is that they grow uncontrollably. When the cancer cells grow too fast, they prevent your organs from working normally. For example, if cancer affects the lungs, the tumor may grow so large it blocks a major airway so that part of the lung is not usable for breathing or an infection may develop because of the blockage.

Cancerous tumors also can spread to different parts of the body. Sometimes a cancerous tumor sheds cells. These cells can be carried to other parts of the body through the blood or the natural fluid around the lung tissue called lymph. The cells can begin to grow uncontrollably in the new location, causing problems in that part of your body. Sometimes other types of cancer spread to the lungs. Though the cancer is in your lungs, this type of tumor is not considered lung cancer.

What Are the Types of Lung Cancer?

There are two main types of lung cancer: small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). A third less common type of lung cancer is called carcinoid.

types of lung cancer chart

Small cell lung cancer (SCLC)

There are two different types of small cell lung cancer: small cell carcinoma and mixed small cell/large cell cancer or combined small cell lung cancer. The types of small cell lung cancer are named for the kinds of cells found in the cancer and how the cells look when viewed under a microscope. Small cell lung cancer is almost always associated with cigarette smoking. Small cell lung cancer is usually treated with chemotherapy.

Non-small cell lung cancer (NSCLC)

Non-small cell lung cancer is more common. It makes up about 80 percent of lung cancer cases. This type of cancer usually grows and spreads to other parts of the body more slowly than small cell lung cancer does. There are three different types of non-small cell lung cancer:

  1. Adenocarcinoma: A form of non-small cell lung cancer often found in an outer area of the lung. It develops in the cells of epithelial tissues, which line the cavities and surfaces of the body and form glands.
  2. Squamous cell carcinoma: A form of non-small cell lung cancer usually found in the center of the lung next to an air tube (bronchus).
  3. Large cell carcinoma: A form of non-small cell lung cancer that can occur in any part of the lung and tends to grow and spread faster than adenocarcinoma or squamous cell carcinoma.

The above subtypes are the most common, but when your lung cancer tumor is looked at under a microscope, it might reveal even more specific information about the subtype. Work with your doctor to understand exactly which type of lung cancer you have and what it means for your treatment options.


Pancoast tumors, also known as superior sulcus tumors, grow in the upper part of the lung and interfere with the structures around it. These tumors are rare and most always non-small cell lung cancer. However, they can be tumors from other diseases like lymphoma or tuberculosis. Pancoast tumors may be treated with chemotherapy, radiation and/or surgery.


Lung carcinoid tumors are uncommon and tend to grow slower than other types of lung cancers. They are made up of special kinds of cells called neuroendocrine cells. They are usually classified as typical or atypical carcinoids. Carcinoids are very rare, slow-growing and most commonly treated with surgery.

Just as each person is unique, each type of lung cancer is different. It is important to know the type of lung cancer you have, sometimes called “your lung cancer profile” because it helps determine what lung cancer treatment options are available.

Watch pulmonologist Dr. Anil Vachani, talk about the different types of lung cancer.

What Causes Lung Cancer?

Anyone can get lung cancer. Lung cancer happens when cells in the lung mutate or change. Various factors can cause this mutation (a permanent change in the DNA sequence of a gene) to happen. Most often, this change in lung cells happens when people breathe in dangerous, toxic substances. Even if you were exposed to these substances many years ago, you are still at risk for lung cancer.

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Learn more about your specific type of lung cancer and treatment options using our My Lung Cancer Treatment Planning Tool

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    Your Profile, Your Goals - Types of Lung Cancer

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    Reviewed and approved by the American Lung Association Scientific and Medical Editorial Review Panel. Last reviewed November 26, 2017.

    Page Last Updated: July 11, 2019

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