|
Your lungs are two sponge-like organs found
in your chest cavity. Your right lung is divided into 3 sections, called
lobes. Your left lung has 2 lobes. It is smaller because your heart
takes up more room on that side of the body. When you breathe, air goes
into your lung through the trachea (windpipe). The trachea
divides into tubes called the bronchi, which divide into smaller
branches called the bronchioles. At the end of the bronchioles
are tiny air sacs known as alveoli. Many tiny blood vessels run
through the alveoli, absorbing oxygen from the inhaled air into your
bloodstream and releasing carbon dioxide. Taking in oxygen and getting
rid of carbon dioxide are your lungs’ main function. A slippery lining,
called the pleura, surrounds the lungs. This lining protects your lungs
and helps them slide back and forth as they expand and contract during
breathing.
Most lung cancers start in the lining of
the bronchi. That is why another term for lung cancer is bronchogenic
cancer. Lung cancer can also form in glands below the lining of the
bronchi, frequently in the periphery of the lungs. Lung cancers are
thought to develop over a period of many years. First, there may be
areas of precancerous changes in the lung. These changes do not form a
mass or tumor. They cannot be seen on an x-ray and they do not cause
symptoms. But, these precancerous changes can be found by analyzing
cells in the lining of the airways of smoke-damaged lungs. Recently,
molecular abnormalities believed to be precancerous have been identified
in cells from individuals at high risk to develop lung cancers (for
example, survivors from one prior lung cancer). These precancerous
changes often progress to true cancer. As a cancer develops, the cancer
cells may produce chemicals that cause new blood vessels to form nearby.
These new blood vessels nourish the cancer cells, which can continue to
grow and form a tumor large enough to see on x-rays. Cells from the
cancer can break away from the original tumor and spread to other parts
of the body. As noted earlier, this process is called metastasis.
Lung cancer is a life-threatening disease because it often spreads in
this way even before it can be detected on a chest x-ray.
Types of Lung Cancer
There are two major types of lung cancer:
- small cell lung cancer (SCLC)
- non-small cell lung cancer (NSCLC).
If a lung cancer has characteristics of
both types it is called a mixed small cell/large cell carcinoma. This is
uncommon. These two types of lung cancer are discussed separately
because they are treated very differently.
Small Cell Lung Cancer
About 13% of all lung cancers are the
small cell type (SCLC), named for the small round cells that make up
these cancers. SCLC tends to spread widely through the body. This is
important because it means that treatment must include drugs to kill the
widespread disease. The cancer cells can multiply quickly, form large
tumors, and spread to lymph nodes and other organs such as the bones,
brain, adrenal glands, and liver. This type of cancer often starts in
the bronchi near the center of the chest. Small cell lung cancer is
almost always caused by smoking. It is very rare for someone who has
never smoked to have small cell lung cancer. Other names for SCLC are
oat cell carcinoma and small cell undifferentiated carcinoma.
Non-small Cell Lung Cancer
The remaining 87% of lung cancers are
non-small cell (NSCLC). There are three sub-types of NSCLC. The cells in
these sub-types differ in size, shape, and chemical make-up.
- squamous cell carcinoma: About
25% - 30% of all lung cancers are squamous cell carcinomas. They are
associated with a history of smoking and tend to be found centrally,
near a bronchus.
- adenocarcinoma: This type
accounts for about 40% of lung cancers. It is usually found in the
outer region of lung. People with one type of adenocarcinoma, known as
bronchioloalveolar carcinoma (sometimes called bronchoalveolar
carcinoma or bronchioalveolar carcinoma) tend to have a better outlook
(prognosis) than those with other types of lung cancer.
- large-cell undifferentiated
carcinoma: This type of cancer accounts for about 10% - 15% of
lung cancers. It may appear in any part of the lung, and it tends to
grow and spread quickly resulting in a poor prognosis.
Other Types of Lung Cancer
In addition to the 2 main types of lung
cancer, other tumors can occur in the lungs. Some of these are
non-cancerous (benign). Carcinoid tumors of the lung account for
fewer than 5% of lung tumors. Most are slow-growing tumors that are
called typical carcinoid tumors. They are generally cured by surgery.
Although some typical carcinoid tumors can spread, they usually have a
better prognosis than small cell or non-small cell lung cancer. Cancers
intermediate between the benign carcinoids and small cell lung cancer
are known as atypical carcinoid tumors.
For more information, about typical and
atypical carcinoid tumors see our document "Lung Carcinoid Tumors."
There are other, even more rare, lung
tumors such as adenoid cystic carcinomas, hamartomas, lymphomas, and
sarcomas. Since these tumors are treated differently from the more
common lung cancers, they are not discussed in this document.
Revised: 02/09/2006
Infomation Provide by www.cancer.org/
|
