What is cancer?

Cancer may seem complex. But at its core, cancer is simple. Normal cells grow and die when your body needs them to. Cancer is what happens when certain cells grow even though your body doesn’t need them.

In many cases, these cancerous cells form a lump or mass called a tumor. Since cancerous cells don’t act like normal cells, tumors can prevent your body from working correctly. Given time, they can also spread, or metastasize, to other parts of the body.

Lung cancer is cancer that starts in the cells that make up the lungs. It isn’t cancer that spreads to the lungs from other parts of the body. This is key because treatment is based on the original site of the tumor. For example: If a tumor begins in the breast and spreads to the lungs, it would be treated as metastatic breast cancer—not lung cancer.

Understanding the lungs

The lungs are two sponge-like organs in your chest. Their job is to bring oxygen into the body and to get rid of carbon dioxide. When you breathe air in, it goes into your lungs through your windpipe (trachea). The trachea divides into two tubes called bronchi, which enter the lungs. These divide into smaller branches called bronchioles. At the end of the bronchioles are tiny air sacs called alveoli. The alveoli move oxygen from the air into your blood. They take carbon dioxide out of the blood. This leaves your body when you breathe out (exhale).

Your right lung is divided into three sections (lobes). Your left lung has two lobes.

Types of lung cancer

There are two main types of lung cancer: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Understanding the differences between these types will help when your doctor talks with you about your diagnosis and treatment.

Non-small cell lung cancer

NSCLC accounts for 85% to 90% of lung cancer cases. There are 3 main subtypes. Each subtype is named for the type of cell it develops in:

• Adenocarcinoma. This is the most common type of lung cancer—particularly among the minority of nonsmokers who get the disease. It tends to appear on the outer edges of the lungs and grows more slowly than the other subtypes.

• Squamous cell carcinoma (epidermoid carcinoma). This type of cancer develops more often in smokers or former smokers than lifetime nonsmokers. It tends to start in the center of the lungs near the bronchial tubes.

• Large cell carcinoma. The least common NSCLC, large cell carcinoma can begin anywhere in the lung. It tends to grow more quickly and spread faster than the other subtypes, which can make it harder to treat.

Despite minor differences, they are often treated in a similar way.

Small cell lung cancer

Small cell lung cancer is much less common than NSCLC. There are two types of small-cell lung cancer: small cell carcinoma (also called oat cell cancer) and combined (small and non-small) cell carcinoma. It's also almost exclusively found in smokers. It tends to grow more quickly than NSCLC. It often spreads to other parts of the body at an earlier stage.

How lung cancer spreads

Lung cancer acts differently in different people. But when it spreads, it tends to go to the same places. The first place it usually appears is in the lymph nodes in the center of the chest. It may also spread to lymph nodes in the lower neck.

Lymph nodes are small clusters of immune system cells.

During later stages, lung cancer may spread to more distant parts of the body, such as the liver, brain, or bones.

Talk with your doctor

If you have questions about lung cancer, talk with your doctor. They can help you understand more about this cancer.