What Is Lung Cancer?

Lung cancer occurs when a tumor grows inside one of your lungs. The cancer can spread to other parts of your body. It's important to catch the cancer early.

Lung cancer accounts for about 20 percent of all cancer deaths, more than any other cancer in the United States. More people die of lung cancer each year than of colon, breast, and prostate cancers combined.

Although men are more likely to die of lung cancer, there are slightly more cases among women. Smoking is the main cause.

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There are two main types of lung cancer: non-small cell lung cancer and small cell lung cancer.

When you have a biopsy, removal of tissue from your lung, a pathologist uses a microscope to look at the cancer cells to establish which type of cancer you have.

The two types of lung cancer grow and spread in different ways and are treated differently. Non-small cell lung cancer usually grows and spreads more slowly than small cell lung cancer.  

Non-small cell lung cancer (NSCLC)

About 80 to 85 percent of lung cancers fall into this category. There are three main types of NSCLC. While there are slight differences among them, they tend to have a similar prognosis (outlook) and are generally treated the same way:

• Adenocarcinoma. This is the most common kind of non-small cell lung cancer. Although mainly occurring in smokers or former smokers, it’s the most common type of lung cancer in people who never smoked. It tends to grow in the outer edges of your lungs, usually more slowly than other types of lung cancer. 
• Squamous cell carcinoma (epidermoid carcinoma). These cancers start in the flat cells lining the inside of your airway, usually in the middle  of your lungs.
• Large cell carcinoma. This type can appear in any part of your lung. It tends to grow and spread early to other organs, which can make it harder to treat.

Small cell lung cancer (SCLC)

Only about 10 to 15 percent of lung cancers fit this group. Small cell lung cancer, also called oat cell cancer, grows and spreads quickly. It is often spotted only when it has spread beyond your lungs.

Although it is rare for this kind of cancer to occur in someone who has never smoked, radon, air pollution, and secondhand smoke can cause the tumor.

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