Figure 1-Copyright© Nucleus Medical Media, Inc.

Cancer is a disease in which cells grow in an abnormal way. Normally, the cells divide in a controlled manner to replace old or damaged cells. If cells keep dividing when new cells are not needed, a mass of tissue called a tumor forms.

Not all tumors are cancer, those that are cancer are called malignant. Cancer tumors invade and damage tissue around them. The cancer cells can also enter the lymph and blood streams, spreading to other parts of the body. Lung cancer is the development of malignant cells in the lung tissue.

Lung Cancer Growth

Lung cancer can start anywhere in the respiratory tract, but it is most commonly found in the cells that form the lining of the bronchi or alveoli. Tumors that grow in the lungs can cause a persistent, worsening cough or shortness of breath. If it grows beyond the lungs, the cancer can penetrate nearby structures, such as the great blood vessels that lead to and from the heart, tissue in and around the heart, or major nerves. The cancer can also spread to the lymph nodes or blood vessels, which can carry cancer cells to other areas of the body. The most common sites for lung cancer to spread to are the lymph nodes in other parts of the body, the liver, bones, or brain.

Lung cancer is categorized by where tumors start, how they grow, and their appearance under a microscope. Lung cancer types include:

  • Non-small cell - This type generally grows and spreads more slowly. Non-small cell lung cancer accounts for about 85% lung cancer cases. The most common types of non-small cell lung cancer are:
    • Adenocarcinoma - Generally found in the outer areas of the lung. Adenocarcinomas arise from cells that form in glandular tissue. They tend to grow slowly, making earlier detection more likely.
    • Squamous cell - Arise from the flat cells that line the inside the respiratory pathways and lungs. These cancers tend to be found near major structures in the airways like the bronchi.
    • Large cell - This type can develop in any part of the lung. It generally grows and spreads faster than the previous types mentioned above.
  • Small cell - This type generally grows more quickly and is mainly associated with smoking. It is more likely to spread to other parts of the body. Small cell cancers are classified as oat cell or combined based on the appearance of cells under the microscope.
  • Carcinoid tumors - Rare type of slow-growing tumor.