Lung Cancer
Medical Author:
Melissa Conrad Stöppler, MD
Medical Editor: Jay W. Marks, MD
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Why Does Lung Cancer Occur in Non-Smokers?
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: Jay W. Marks, MD
While cigarette smoking is
an undisputed cause of lung
cancer, not all cases
of lung cancer occur in smokers or former smokers. Each year, over 170,000
Americans develop lung cancer, and approximately 10% of lung cancers,
or 17,000 cases, occur in non-smokers. Although not every non-smoker suffering
from lung cancer will have an identifiable risk factor for development of the disease, a number of conditions and circumstances have been identified that will
increase a non-smoker’s chance of developing lung cancer.
Passive smoking,
or the inhalation of tobacco smoke from other smokers
sharing living or working quarters, is an established risk factor for the
development of lung cancer. Non-smokers who reside with a smoker have a 24%
increase in risk for developing lung cancer when compared with other
non-smokers. Each year, up to 3,000 lung cancer deaths are estimated to occur in
the U.S. that are attributable to passive smoking. For more, please read
the
Dangers Secondhand Smoke article.
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What is lung cancer?
Cancer of the lung, like all cancers, results from an abnormality in the body's
basic unit of life, the cell. Normally, the body maintains a system of checks
and balances on cell growth so that cells divide to produce new cells only when
new cells are
needed. Disruption of this system of checks and balances on cell growth results
in an uncontrolled division and proliferation of cells that eventually forms a
mass known as a tumor.
Tumors can be benign or malignant; when we speak of "cancer," we are referring
to those tumors that are malignant. Benign tumors usually can be removed and do
not spread to other parts of the body. Malignant tumors, on the other hand, grow
aggressively and invade other tissues of the body, allowing entry of tumor cells
into the bloodstream or lymphatic system and then to other sites in the body.
This process of spread is termed metastasis; the areas of tumor growth at these
distant sites are called metastases. Since lung cancer tends to spread or
metastasize very early after it forms, it is a very life-threatening cancer and
one of the most difficult cancers to treat. While lung cancer can spread to any
organ in the body, certain organs -- particularly the adrenal glands, liver,
brain, and bone -- are the most common sites for lung cancer metastasis.
The lung also is a very common site for metastasis from tumors in other parts
of the body. Tumor metastases are made up of the same type of cells as the
original (primary) tumor. For example, if prostate cancer spreads via the
bloodstream to the lungs, it is metastatic prostate cancer in the lung and is
not lung cancer.
Lung Cancer Picture
The principal function of the lungs is to exchange gases between the air we breathe and the blood. Through the lung, carbon dioxide is removed from the bloodstream and oxygen from inspired air enters the bloodstream. The right lung has three lobes, while the left lung is divided into two lobes and a small structure called the lingula that is the equivalent of the middle lobe on the right. The major airways entering the lungs are the bronchi, which arise from the trachea. The bronchi branch into progressively smaller airways called bronchioles that end in tiny sacs known as alveoli where gas exchange occurs. The lungs and chest wall are covered with a thin layer of tissue called the pleura.
Lung cancers can arise in any part of the lung, but 90%-95% of cancers of the lung are thought to arise from the epithelial cells, the cells lining the larger and smaller airways (bronchi and bronchioles); for this reason, lung cancers are sometimes called bronchogenic cancers or bronchogenic carcinomas. (Carcinoma is another term for cancer.) Cancers also can arise from the pleura (called mesotheliomas) or rarely from supporting tissues within the lungs, for example, the blood vessels.
Next: How common is lung cancer? »
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