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 ten per cent 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 cancer of the lung?
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
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 refer to those tumors that are considered malignant. Benign tumors can usually 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 in its course, 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 is also 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, or 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 the exchange of 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. 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, or lining cells of the larger and smaller airways (bronchi and bronchioles); for this reason, lung cancers are sometimes called bronchogenic carcinomas or bronchogenic cancers. Cancers can also arise from the pleura (the thin layer of tissue that surrounds the lungs), called mesotheliomas, or rarely from supporting tissues within the lungs, for example, blood vessels.
Next: How common is lung cancer? »
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