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What Is Lung Cancer?

Reviewed by: HU Medical Review Board | Last reviewed: January 2017.

Cancer is a disease that begins at the cellular level. The cells are the building blocks of all the tissue in the body, and in their healthy state, they grow and divide as the body needs them to maintain the current structure. As cells get old or become damaged, they die, and new cells replace them. Cancer develops when the cells become abnormal, reproduce at high rates, and create tumors. Cancerous tumors can also invade surrounding tissues and may spread to other areas of the body.1

What is lung cancer?

Cancer types are named for the organ in which they originate. Lung cancer is a cancer that begins in the lungs, the main organs of the respiratory system. The respiratory system brings oxygen from the air into the body and removes carbon dioxide from the blood.2

Most lung cancers are carcinomas – cancers that start in the cells that line the inner and outer surfaces of the body. Lung cancers are categorized as small cell lung cancer or non-small cell lung cancer, named for their appearance under a microscope. These different types of lung cancer grow and develop differently and are treated differently. The most common is non-small cell lung cancer.1,2

How does lung cancer begin?

All cells have coded instructions in their genes. When changes occur to the genes, the cells change their normal behavior. Changes in the genes cause normal cells to become cancer cells. Genetic changes can be inherited, but in the case of lung cancer, the genetic changes that cause cancer to develop can be caused by other factors, such as environmental exposure to pollutants like tobacco smoke. The most common cause of lung cancer, by far, is tobacco smoking.1,2

Each cancer is unique with different genetic changes, and as the cancer grows, additional changes occur in the genes. Scientists have found that there are certain changes, or mutations, that commonly occur in many types of cancers. These mutations are often a target for potential treatments to stop the cancer.1

How does lung cancer spread?

When cancer spreads from its original location to other parts of the body, it is called metastatic cancer. The process of the cancer spreading is called metastasis. In metastasis, cancer cells can break off from the original tumor and travel through the body’s blood stream or lymphatic system to form tumors elsewhere in the body. Metastatic lung cancer can affect the adrenal gland, liver, bones, and the brain. Despite having tumors in different areas, metastatic lung cancer is still considered lung cancer – not liver cancer or brain cancer – because the cancer cells originated from the lung. The cells of metastatic tumors look basically the same as the cells of the original cancer under a microscope.1

How is lung cancer treated?

The treatment for lung cancer is based on the stage of the disease and the category. Staging determines how advanced the cancer is and if and how it has spread to other parts of the body. The two categories of lung cancer are non-small cell lung cancer and small cell lung cancer. Depending on the category and the stage of lung cancer, treatment may involve surgery, chemotherapy, radiation, targeted treatments, and/or immunotherapy.3

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