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 sacs where oxygen is transferred to the bloodstream.

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 is lung cancer?

Lung cancer forms in the tissues of the lungs, most often in the cells that line air passages. It occurs when these cells start to grow and multiply uncontrollably, usually as a result of exposure to toxins such as tobacco smoke, radiation and asbestos. However, 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%.

Symptoms

Lung cancer symptoms vary from person to person. Early on in the disease, people with lung cancer may not have any symptoms. Often, symptoms are easily confused with common respiratory illnesses such as bronchitis or pneumonia, delaying an accurate diagnosis.

If you have symptoms of lung cancer, they may include:

• A cough that does not go away and gets worse over time
• Constant chest pain, often made worse by deep breathing, coughing, or laughing
• Arm or shoulder pain
• Coughing up blood or rust-colored phlegm
• Shortness of breath, wheezing, or hoarseness. This can happen when a lung tumor blocks major airways within the lungs. Lung cancer can also lead to the accumulation of fluid in the chest cavity (pleural effusion), which can make it harder for the lungs to expand fully.
• Repeated episodes of pneumonia or bronchitis
• Swelling of the neck and face. This occurs when the tumor compresses a large vein, the superior vena cava, that moves blood to the heart from the head and arms
• Loss of appetite and/or weight loss
• Feeling weak or tired
• Widening of the fingertips and nailbed also known as “clubbing.” This symptom is common in non-small cell lung cancer cases, but rare for small cell lung cancer.

If lung cancer spreads to other parts of the body, it may cause:

• Bone pain
• Arm or leg weakness or numbness
• Headache, dizziness, or seizure
• Balance problems or an unsteady gait
• Jaundice (yellow coloring) of skin and eyes
• Swollen lymph nodes in the neck or shoulder

These symptoms do not always mean you have lung cancer. However, it is important to discuss any lung cancer symptoms with your doctor, since they may also signal other health problems.

Types of lung cancer

Lung cancers are classified into two major groups according to the type of cancer cells that make up the tumor. 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, accounting for approximately 85% of lung cancers. Non-small cell lung cancers arise from the lungs’ epithelial cells, a type of cell that lines the surface of organs, including the airways. They tend to start as solitary nodules, but 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: Adenocarcinoma is a type of cancer that begins in glandular cells that line the alveoli. When healthy, these cells make mucus. Lung adenocarcinomas are usually caused by cigarette smoking, although this type of cancer can often occur in nonsmokers, women at younger ages. Adenocarcinoma often occurs along the outer edges of the lungs, and it generally affects smaller airways like the alveoli and bronchioles.
• Squamous cell carcinoma: This lung cancer begins in thin, flat squamous epithelial cells that line the airways of the lungs. Cigarette 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. These cells receive signals from the nervous system to produce hormones.

Small cell lung cancer

Small cell lung cancer makes up about 15% of lung cancers and almost always is caused by cigarette smoking. They 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 until after it has spread to other parts of the body. This means that surgery is generally less effective for small cell lung cancer than non-small cell lung cancer.

Other, rarer types of lung cancer include:

• Lung carcinoid tumors: Carcinoid tumors affect special cells in the lungs called neuroendocrine cells. When healthy, these cells receive signals from the nervous system to produce hormones important to the function of the lungs. This type of cancer is rare and is treated differently from small cell and non-small cancers.
• Cancers affecting the lymph nodes, supportive tissue, or smooth muscles of the lungs are also rarer and require different treatment

What does it mean for lung cancer to 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 and interfere with the lungs’ normal function. Additionally, part of the lung tumor may break off and travel through to other areas of the body. When this occurs, it is called metastasis.

Lung cancer frequently spreads, or metastasizes, through the lymphatic system. Lymph is a clear fluid that contains immune cells to help fight infections. It enters and drains body tissues through a network of lymphatic vessels that connects to various body parts. Lymph nodes are small, bean-shaped organs that link lymph vessels. They often trap cancer cells that have entered the lymphatic system. Once in the lymphatic system, the cancer cells can develop into tumors within lymph nodes, or they can travel to other parts of the body.

Cancer cells can also metastasize through 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. Even if lung cancer has spread to another organ, it 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, colon cancer with lung metastases is called metastatic colon cancer.

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 (HIV)
  

Learn more about lung cancer:

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