Lung Cancer

Approved by the Cancer.Net Editorial Board, 12/2022

Lung cancer affects more than 200,000 people in the United States and an estimated 2.3 million people around the world each year. Although cigarette smoking is the main cause, anyone can develop lung cancer. Lung cancer is highly treatable, no matter the size, location, whether the cancer has spread, and how far it has spread.

Because lung cancer has been associated with smoking, patients may feel that they won’t receive much support or help because they believe that others will think that their behavior caused the disease. The truth is that most smokers do not develop lung cancer, and not all people diagnosed with lung cancer have been tobacco smokers. Lung cancer is a disease that can affect anyone. In fact, most people who get lung cancer today have either stopped smoking years earlier or never smoked.

When a person inhales, the lungs absorb oxygen from the air and bring the oxygen into the bloodstream for delivery to the rest of the body. As the body’s cells use oxygen, they release carbon dioxide. The bloodstream carries carbon dioxide back to the lungs, and the carbon dioxide leaves the body when a person exhales.

The lungs contain many different types of cells. Most cells in the lung are epithelial cells. Epithelial cells line the airways and make mucus, which lubricates and protects the lung. The lung also contains nerve cells, hormone-producing cells, blood cells, and structural or supporting cells.

There are 2 main classifications of lung cancer: small cell lung cancer and non-small cell lung cancer (NSCLC). These 2 types are treated differently. This guide contains information about NSCLC. Learn more about small cell lung cancer in a different guide. This website also offers a separate guide on neuroendocrine tumors of the lung. 

NSCLC begins when healthy cells in the lung change and grow out of control, forming a mass called a tumor, a lesion, or a nodule. This can begin anywhere in the lung. The tumor can be cancerous or benign. When a cancerous lung tumor grows, it may shed cancer cells. These cells can be carried away in blood or float away in the fluid, called lymph, that surrounds lung tissue. Lymph flows through tubes called lymphatic vessels that drain into collecting stations called lymph nodes.

Lymph nodes are the small, bean-shaped organs that help fight infection. They are located in the lungs, the center of the chest, and elsewhere in the body. The natural flow of lymph out of the lungs is toward the center of the chest, which explains why lung cancer often spreads there first. When a cancer cell moves into a lymph node or to a distant part of the body through the bloodstream, it is called metastasis.

There are different types of NSCLC. It is important to know the type of NSCLC because it can change treatment options. Doctors determine which type of NSCLC a person has based on the way the cancer looks under a microscope and the kind of cells the cancer starts in.

This is what normal lung tissue looks like:

The different types of NSCLC are:

Adenocarcinoma. This type of NSCLC begins in the epithelial cells that line the outside of the lungs. These cells make mucus. It is the most common type of lung cancer at about 40% of all NSCLC cases.

Squamous cell carcinoma. This type of cancer starts in the squamous cells, which are flat cells that line the inside of the lungs. About 30% of all NSCLC cases are squamous cell carcinoma.

Large cell carcinoma. The cells in large cell carcinoma do not look like adenocarcinoma or squamous cell carcinoma, instead they look like large cells. This is the least common type of NSCLC and as diagnostic tools get better, more large cell carcinomas are being classified as adenocarcinoma or squamous cell carcinoma.

NSCLC-NOS (not otherwise specified) or NSCLC undifferentiated. Sometimes it is difficult for doctors to determine the type of NSCLC even after testing.

Images used with permission from the College of American Pathologists.