What Is Non-Small Cell Lung Cancer?

This content has been reviewed and approved by

Chandra P. Belani, MD
Deputy Director, Penn State Cancer Institute
Miriam Beckner Professor of Medicine
Penn State University School of Medicine

Lung cancer is the second most commonly diagnosed cancer in men and women in the United States, according to the American Cancer Society (ACS).

Lung cancer is a growth of abnormal cells that usually starts in the lining of the bronchi. However, it can also begin in the trachea, bronchioles, or alveoli. Lung cancers are believed to develop over a period of weeks or months to years.

Approximately 1.2 million new cases of lung cancer are diagnosed worldwide every year. It will account for an estimated 15 percent of all new cancer cases in men and 14 percent in women in 2010, according to the ACS.

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Structure of the Lungs

Your two lungs are the cornerstone of your respiratory system. The right lung contains three lobes and is slightly larger than the left, which contains two lobes. Air travels from your nose or mouth through your trachea, or windpipe, then through two main air passages called bronchi into your lungs. From there, the air moves through smaller branches of the lungs called bronchioles to the millions of air sacs that extract the oxygen from the air. These sacs are called alveoli. From the alveoli, the oxygen is carried from your bloodstream throughout your body.

Lung cancer is a growth of abnormal cells that usually starts in the lining of the bronchi. However, it can also begin in the trachea, bronchioles, or alveoli. Lung cancers are believed to develop over a period of weeks or months to years. 

What are the Main Types of Lung Cancer?

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer accounting for 87 percent of all cases, with small cell lung cancer comprising the remaining 13 percent. Non-small cancer grows more slowly than small cell cancer, but does not respond as well to chemotherapy. Surgery is the mainstay of treatment for NSCLC.

What are the Types of Non-Small Cell Lung Cancers?

There are several types of non-small cell lung cancer. The most common are:

• Squamous cell carcinoma (also called epidermoid carcinoma) - The most common type of lung cancer in men. It often begins in the bronchi (airways). It usually does not spread as quickly as other types of lung cancer.
• Adenocarcinoma - Adenocarcinoma usually begins along the outer edges of the lungs and under the lining of the bronchi. This type begins in cells that secrete substances, such as mucus. It is the most common type of lung cancer in women and in people who have never smoked.
• Large cell carcinomas - A group of cancers with large, abnormal-looking cells. These tumors usually begin along the outer edges of the lungs.
• Bronchiole-alveolar carcinoma - A relatively rare form of adenocarcinoma that seems to be increasing. It is often mistaken for a lung infection.
• Undifferentiated carcinoma - It involves abnormal-looking cancer cells that tend to multiply quickly and do not fit into any of the above categories.

It is important to find out what kind of lung cancer you have because the different types may involve different regions of the lung. Plus, your treatment depends on the type of lung cancer. Sometimes, however, it’s difficult to determine whether you have small cell lung cancer or non-small cell lung cancer. In these cases, your doctor may need to perform another biopsy.