How Lung Cancer Develops

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To learn how lung cancer develops, it is helpful to understand first how the lungs work. Here you'll find the basics on lung function and how cancer can develop in the lung.

The primary purpose of our two lungs is to bring oxygen into the body and to push carbon dioxide, which forms as a waste product of the body’s cells, out. Each of our lungs has sections called lobes—two in the left lung and three in the right lung. When we inhale, air enters our nose or mouth and goes down our trachea. The trachea branches into two sets of bronchial tubes, each one taking air to a lung. Once inside the lung, the air makes its way into smaller and smaller branched tubes, called bronchioles, until it finally enters the alveoli, small balloon-like sacs. Within these sacs, materials such as carbon dioxide and oxygen are transferred between the bloodstream and the air.1

Lung anatomy diagramThe lungs are made up of many different types of cells. Most of these cells are epithelial cells. These line the airways and make mucus to lubricate and protect the lungs. The lungs also contain blood cells, nerve cells, hormone-producing cells, and structural cells.2

A thin membrane called the pleura covers the outside of each lung and lines the inside wall of the chest cavity. This creates a sac called the pleural cavity. The pleural cavity normally contains a small amount of fluid that helps the lungs move smoothly in the chest when we breathe.1

Development of lung cancer

Normally, the cells in our lungs and other parts of our body have a specific growth and death cycle that keeps the number of cells in check. Cancer, of any kind, develops when a set of specific changes, called mutations, develop in a previously normal cell. When the set of mutations affects genes in ways that change the natural growth and death cycles of cells, unregulated cell division can result in too many cells. It's like a car where the gas pedal gets stuck or the brakes don’t work—the cells just keep dividing with nothing to stop them.

The mutated and abnormally multiplying cells form a mass called a tumor, neoplasm, or lesion. In the case of lung cancer, this mass might be detected as a nodule on a chest X-ray or CT scan. The mass can be benign, or it can be malignant.

Lung cancer metastasis illustration

When the tumor cells are able to invade normal tissues, the tumor is considered to be malignant. When the malignant cells originally come from the lung, we call it lung cancer.

Spread of Cancer

The spread of cancer from one part of the body to another is known as metastasis, and the tumors formed by those cancer cells that have spread are called metastases. Lung cancer metastases can spread to lymph nodes around the lungs, and they can also travel through the bloodstream to other organs, such as bones, adrenal glands, and the brain.

Sometimes cancer starts in other parts of the body and spreads to the lung. That is considered metastasis of the original type of cancer, not lung cancer. Only cancer that starts in the lung is considered lung cancer.2


  1. Non-Small Cell Lung Cancer Treatment (PDQ®). National Cancer Institute website. Updated May 12, 2015. Accessed February 22, 2016.
  2. Lung Cancer – Non-Small Cell: Diagnosis. American Society of Clinical Oncology website. Accessed February 22, 2016.