Lung cancer is the most common cause of cancer-related deaths and second most common cancer in both men and women in the United States. According to the National Cancer Institute, about 234,000 people in the U.S. are diagnosed with the disease each year. While most cases are linked to tobacco smoking, a growing number of diagnoses are among non-smokers, especially among women. Most lung cancers are diagnosed after the disease has spread. As a result, the five-year survival rate for lung cancers is just 19%.

What are the types of lung cancer?

Lung cancers are classified into two major groups according to the type of cancer cells that make up the tumor. They are divided into two main categories: Small cell lung cancer and Non-small cell lung cancer. There are significant differences in the prognosis and treatment for each category.

Non-small cell lung cancer

This is the most common type of lung cancer and accounts for approximately 85% of lung cancers. It arises from the lungs’ epithelial cells, a type of cell that lines the surface of organs, including the airways. These cancers tend to start as solitary nodules. As they grow they may invade surrounding structures or spread (metastasize) to lymph nodes inside the chest as well as to distant organs.

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

• Adenocarcinoma: This begins in glandular cells that line the alveoli. When healthy, these cells make mucus. The main cause for development of lung adenocarcinomas is tobacco smoking, although this cancer type can often occur in nonsmokers, women and at younger age. Adenocarcinoma often occurs in the more peripheral parts of the lung.
• Squamous cell carcinoma: This lung cancer begins in thin, flat squamous epithelial cells that line the airways of the lungs. Tobacco smoking is its main cause and it tends to arise in the more central regions of the lungs. Squamous cell carcinoma is also called epidermoid carcinoma.
• Large cell carcinoma: Large cell carcinoma is a less common type of non-small cell lung cancer. It tends to grow rapidly and may spread early. It usually originates from neuroendocrine cells present in the lungs.

Small cell lung cancer

Small cell lung cancer makes up about 15% of lung cancers and almost always is caused by tobacco smoking. It often starts in the more central portions of the chest. They also grow and spread quickly to other parts of the body, including the lymph nodes. Because it is so aggressive, it is usually not found when it is confined to a single area of the lung. Therefore, surgery is used less often for small cell lung cancer than non-small cell lung cancer.

Cancer grows in lungs, may spread

When lung cancer is small and at an early stage, it usually does not cause symptoms. However, once the disease grows, it may damage surrounding tissue, interfering with the lungs’ normal function and causing symptoms such as hemoptysis (coughing up blood), shortness of breath or pain.

Lung cancer frequently spreads, or metastasizes through the lymphatic system. Lymph is a clear fluid that is drained from our tissues and contains immune cells that help fight infection. It travels through your body in lymphatic vessels. Lymph nodes are small, bean-shaped organs that link lymph vessels. They often trap cancer cells that have spread to the lymphatic system.

Cancer cells can spread to other parts of your body through the bloodstream, as well. When lung cancer spreads to other organs such as the liver or bone, it is known as stage IV lung cancer or metastatic lung cancer. Cancer that has spread to another organ is still referred to as lung cancer. Whether or not a lung cancer has spread to lymph nodes or to other organs significantly influences how the tumor is treated.

What are lung metastases?

Sometimes, a tumor starts in another part of the body and then spreads, or metastasizes, to the lungs. These tumors are called lung metastases, and they are not the same as lung cancer. In these cases, they are the type of cancer where they came from. For example, a colon cancer with lung metastases is called metastatic colon cancer.

Lung anatomy

When you breathe in, oxygen comes through your mouth and nose and then travels through the trachea, or windpipe. The trachea divides into two tubes called bronchi, which take the oxygen to the left and right lungs. Inside the lungs are smaller branches called bronchioles and alveoli, tiny air sacks where oxygen is transferred to the blood stream.

Each lung is divided into sections called lobes. The right lung has three lobes and the left lung has two lobes. The left lung is smaller than the right lung because the heart is also located in the left side of the chest. Each lobe can be further divided into bronchopulmonary segments.

The pleura is a thin membrane that covers the outside of each lung and lines the inside wall of the chest. The space between the lungs and the chest wall usually contains a very small amount of fluid that allows the lungs to move smoothly during breathing.

What are the risk factors for lung cancer?

A risk factor is anything that increases the chance that a person will develop a particular disease. The main risk factors for lung cancer are:

• A history of or current tobacco use
• Exposure to second-hand smoke
• Exposure to asbestos, arsenic, chromium or other chemicals
• Radiation exposure, including radiation therapy to the breast or chest and radon exposure.
• Living in an area with air pollution
• A family history of lung cancer
• Infection with the human immunodeficiency virus.
  

Learn more about lung cancer:

• Lung cancer symptoms
• Lung cancer diagnosis
• Lung cancer treatment
• Lung cancer research