About Lung Cancer

How Lungs Function

The respiratory system is made up of organs involved in gas exchange (oxygen and carbon dioxide) and consists of the nose, pharynx, larynx (voice box), trachea (windpipe), bronchi and lungs. The lungs absorb oxygen, which cells need in order to live and perform their normal functions. Lungs exchange oxygen for carbon dioxide, a waste product of the body’s cells.


The lungs are a pair of cone-shaped organs. They occupy most of the chest, or thorax (the part of the body between the base of the neck and the diaphragm). The lungs surround the heart and are protected by the ribcage, or chest wall.

The lungs and chest wall are lined by a membrane called the pleura and separated from each other by the mediastinum, an area that contains the heart and its large blood vessels (aorta, vena cavae and pulmonary artery), trachea, esophagus (swallowing tube), thymus and lymph nodes.

The right lung is slightly larger than the left lung. Both lungs are comprised of sections called lobes and each lobe is further divided into segments. The right lung has three lobes (right upper, middle and lower) and 10 segments, while the left lung has two lobes (left upper and lower) and eight segments. Each lobe and segment has its own airway transmission (bronchus) and blood supply (pulmonary artery and pulmonary vein).

Because the lung is divided into lobes and further subdivided into segments, thoracic surgeons are able to anatomically remove certain portions of the lung (lobectomy or segmentectomy) if needed, including lymph nodes contained in that segment.

When we inhale, air enters our bodies through the nose or mouth and travels down the throat through the larynx and trachea. It then enters the lungs through two structures called main-stem bronchi. One main-stem bronchus leads to the right lung while the other travels to the left lung.

In the lungs, the main-stem bronchi divide into smaller bronchi and then into even smaller tubes called bronchioles. Bronchioles end in tiny air sacs called alveoli, which look like a cluster of grapes when viewed under a microscope.

There are over three million alveoli in normal lungs. The alveoli are covered by blood vessels (capillaries), where the exchange between oxygen and carbon dioxide occurs.

For an additional diagram of the lungs, visit the National Cancer Institute

Understanding Lung Cancer

Billions of cells do different jobs throughout our body. Normal cells grow, divide and organize in an orderly way. Cells die and are replaced by new cells continuously.

A tumor develops when cells in the body begin to divide and change without order or control. If cells keep dividing uncontrollably, a mass of tissue forms into a growth or tumor.

Not all tumors are cancerous. Tumors that are not cancerous are considered benign. Malignant tumors are cancerous and can invade nearby tissue and spread, or metastasize, to other parts of the body.

Types of Lung Cancer

Lung cancer is divided into two main categories: Small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC).

The main focus here is on NSCLC because it is the most common form of lung cancer, representing 87 percent of patients with the disease. SCLC is a more aggressive form of lung cancer which occurs less frequently, in approximately 13 percent of patients. Because it is more aggressive and usually advanced at diagnosis, SCLC is typically treated with chemotherapy and radiation therapy. Surgery is involved occasionally. Read more about SCLC.

NSCLC is further divided into three subtypes: adenocarcinoma (40 percent), squamous cell carcinoma (30 to 35 percent) and large cell carcinoma (15 to 20 percent). All three NSCLC subtypes tend to metastasize, or spread, more slowly than SCLC. Of particular importance to thoracic surgeons and oncologists is the lung cancer stage, rather than the subtype, which helps determine a patient’s overall prognosis and treatment plan.

  • Adenocarcinoma is the most common subtype of NSCLC. It arises from the alveolar surface and in the mucus-producing glands of the lung. Typically, most tumors of this type are found near the periphery of the lung.
  • Adenocarcinoma with lepidic growth, previously called bronchioloalveolar carcinoma (BAC), is a rare form of adenocarcinoma that occurs in three percent of all lung cancer patients. It typically presents in younger patients, and is more common in women and nonsmokers. It tends to be less aggressive but can recur within the lung.
  • Squamous cell carcinoma is found in the mucous lining of the bronchial tubes. These tumors tend to grow more slowly, are more central in location, and are more common in men.
  • Large-cell undifferentiated carcinoma occurs at the outer edges of the lungs and can grow quickly.

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