Molecular diagnosis

Lung cancer traditionally is categorized by the type of cell where it begins. Today, doctors can also diagnose the disease on a molecular level.

This approach usually looks for mutations in the DNA of cancer cells and/or proteins produced by the cells. There are hundreds of different molecular diagnoses, including mutations to the EGFR, ALK, KRAS and ROS1 genes.

These molecular subtypes can impact how quickly the disease grows and spreads. They also can predict how the disease will respond to specific treatments, including different types of chemotherapy, targeted therapy and immunotherapy. By diagnosing a patient’s disease on a molecular level, doctors can design treatment plans with the best chance of fighting each patient’s specific cancer.

Cellular diagnosis

The traditional diagnosis based on the type of cell where the cancer started can still help doctors understand the patient’s condition and make a treatment plan. The two main categories are:

• Non-small cell lung cancer, which accounts for about 85% of lung cancer cases. It arises from the lungs’ epithelial cells, a type of cell that lines the surface of organs. There are several types of non-small cell lung cancer based on the type of epithelial cell where the disease begins, including adenocarcinoma, squamous cell carcinoma and large cell carcinoma.
• Small cell lung cancer, which 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. It usually grows and spreads quickly to other parts of the body, including the lymph nodes. Because it is so aggressive, surgery is used less often for small cell lung cancer than non-small cell lung 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.

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.

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 cancer statistics

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, more than 230,000 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 22%, though cases that are caught before the disease has spread have a much higher survival rate.

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
• Living in an area with air pollution
• A family history of lung cancer
• Infection with the human immunodeficiency virus (HIV)
• Radiation exposure, including radiation therapy to the breast or chest, and radon exposure. This is a minor risk factor and the benefits of radiation therapy as a cancer treatment far outweigh the risks.

In some cases, lung cancer can be passed down from one generation to the next. Genetic counseling may be right for you. Visit our family history  site to learn more about genetic counseling and testing.