Lung cancer is any
cancerous growth in lung
tissue. The cancers can arise in the lungs, or be
metastic (spread) from other sources.
Causes
Lung cancers form in the
epithelium (lining) the
bronchi ( tubes by which
air passes to the lungs), or in the fine
air sacs that terminate the passage.
The most
common forms originate in
bronchial epithelium that has been altered by long exposure to
cigarette smoke to form less specialized cells known as
squamous cells (flat cells).
The cells that do not become flattened still possibly can become cancerous. The epithelial cells of bronchi may also undergo certain
transformations to give rise to
adenocarcinomas, but these
tumors do not appear to be related to
cigarette smoking.
Types
adenocarcinoma - account for some 25 to 30 percent of lung cancers; it is the most common type of lung cancer in the
United States. Cells of adenocarcinoma are
cube- or
column-shaped, and they form structures that resemble
glands (hence the name, aden means gland) and are sometimes
hollow. Tumors often originate in the smaller, peripheral bronchi;
symptoms at the time of
diagnosis often reflect
invasion of the
lymph nodes, pleura, the other lung or the
metastasis to other
organs.
large-cell carcinomas -20 percent. There is some
dispute as to whether it is a
distinct type of cancer or merely a group of atypical squamous-cell carcinomas and adenocarcinomas.
Large-cell carcinomas generally originate in the peripheral areas of the lung.
small-cell carcinomas - Cancers of this type have tumors that
secrete hormones.
Alveolar - The
alveoli are small air sacks in the lungs where
oxygen is transferred into
blood cells. Cancer of the alveoli is any cancer arising in these air sacks
Squamous cell carcinomas - The form differentiation, from specific bronchial epithelium to flattened cells can give rise to cancer, becoming squamous-cell
carcinomas. Cancer of this type typically arises on the
skin,
lips, and
throat.
Symptoms
In the
earliest stages of lung cancer there are often no symptoms. In later stages symptoms may include
coughing,
chest pain,
shortness of breath,
blood in the
sputum, and repeated episodes of
pneumonia;
weight loss, loss of
appetite, and
weakness may also accompany the
disease. Sometimes the first symptoms result from the metastasis of the tumor to other parts of the body.
Cures
The main
treatments for lung cancer are
surgery,
chemotherapy, and
radiation. The choice of treatment depends on the patient's general
health, the stage or extent of the disease, and the type of cancer. Surgery is the preferred treatment for patients with non-small-cell carcinoma. Many patients, however, have
heart or
respiratory diseases that limit their ability to tolerate surgery. Surgery is not the main treatment for patients with cancer in both lungs or for those whose cancer has
metastasized to distant organs. It is of no value in most cases of small-cell carcinoma; chemotherapy or radiation therapy, or both, are usually used.
Small-cell carcinoma responds better to chemotherapy than do other types of lung cancer.
Treatment is most effective in the early stages of the disease, when the tumor is small and the patient is still relatively
healthy. Because most patients have extensive lung cancer at the time of diagnosis, however, the outlook is generally poor. A majority of patients
die of the disease within one year of its
detection, and only some 10 percent
survive for five years or more.
Works cited
"respiratory disease" Encyclopædia Britannica Online.
On-line Medical Dictionary . (http://www.graylab.ac.uk/)