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Note: This document is only for the
non-small cell type of lung cancer. The treatment for each type of lung
cancer (small cell vs. non-small cell) is very different, so much of
the information for one type will not apply to the other type. If you
are not sure which type of lung cancer you have, it is very important
to ask you doctor so you can be sure the information you receive is
correct.
Lung cancer is a cancer starts in the lungs. In order to
understand lung cancer, it helps to know about the normal structure and
function of the lungs.
The Lungs
The lungs are two sponge-like organs found in the chest. The
right lung has 3 sections, called
lobes. The left lung has 2 lobes, as shown in the picture
below. The left lung is smaller because the heart takes up more room on
that side of the body. The lungs bring air in and out of the body,
taking in oxygen and getting rid of carbon dioxide gas, a waste
product.

The lining around the lungs, called the pleura, helps to
protect the lungs and allows them to move during breathing. The
windpipe (trachea)
brings air down into the lungs. It divides into tubes called bronchi (singular,
bronchus)
which divide into smaller branches called bronchioles. At the
end of these small branches are tiny air sacs known as alveoli.
Start and Spread of Lung Cancer
Most lung cancer starts in the lining of the bronchi, but it
can also start in other parts of the lung. Lung cancer often takes many
years to develop. First, there may be areas of pre-cancerous changes in
the lung. These changes are not a mass or tumor. They can’t be seen on
an x-ray and they don’t cause symptoms.
Over time, these pre-cancerous areas may go on to become true
cancer and make chemicals that cause new blood vessels to form nearby.
These new blood vessels nourish the cancer cells and allow a tumor to
form. Finally, the tumor becomes large enough to show up on an x-ray.
At some point, cancer cells can break away and spread to other
parts of the body in a process called metastasis. Lung cancer is a
life-threatening disease because it often spreads in this way before it
is found.
One of the ways lung cancer can spread is through the
lymphatic system. Lymphatic vessels are like veins but carry lymph
fluid instead of blood. Lymph is a clear fluid that contains tissue
waste products and immune system cells. Lung cancer cells can enter
lymphatic vessels and begin to grow in lymph nodes around the bronchi
and in the the area between the lungs. When lung cancer cells have
reached the lymph nodes, they are more likely to have spread to other
organs of the body too. Staging and decisions about lung cancer
treatment are based on whether or not the cancer has spread to the
nearby lymph nodes. These topics are discussed later in the section,
"How
Is Non-Small Cell Lung Cancer Staged?"
Types of Lung Cancer
There are 2 main types of lung cancer and they are treated
differently.
- small cell lung cancer (SCLC)
- non-small cell lung cancer (NSCLC)
If the cancer has features of both types, it is called mixed
small cell/large cell cancer.
The information here only covers non-small cell lung cancer.
Small cell lung cancer is covered in a separate document.
Other types of tumors can grow in the lungs, too. Some of
these are not cancer and others are cancerous. Carcinoid tumors, for
example, are slow-growing and usually cured by surgery. The American
Cancer Society has more information about lung carcinoid tumors. To
learn about these tumors, see our document Lung
Carcinoid Tumor.
Non-Small Cell Lung Cancer
(NSCLC)
About 85% to 90% of all lung cancers are of the non-small cell
type. There are 3 sub-types of NSCLC. The cells in these sub-types
differ in size, shape, and chemical make-up.
Squamous cell
carcinoma: About 25% to 30% of all lung cancers
are this kind. They are linked to smoking and tend to be found in the
middle of the lungs, near a bronchus.
Adenocarcinoma:
This type accounts for about 40% of lung
cancers. It is usually found in the outer part of the lung.
Large-cell
(undifferentiated) carcinoma: About 10% to 15% of
lung cancers are this type. It can start in any part of the lung. It
tends to grow and spread quickly, which makes it harder to treat.
Other Types of Lung Cancer
Along with the 2 main types of lung cancer, other tumors can
be found in the lungs. Keep in mind that cancer that starts in other
organs (such as the breast, pancreas, kidney, or skin) and spreads
(metastasizes) to the lungs is not the same as lung cancer. For
example, cancer that starts in the breast and spreads to the lungs is
still breast cancer, not lung cancer.
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