Lung Cancer
To Your Health -- CHRC Newsletter
Winter 2001
In the United States lung cancer is the most common cause of death from cancer, both in men and women. Approximately 160,000 people died last year from this disease. This represents a 600% increase in the age-adjusted death rate compared to the year 1930. This dramatic increase in the death rate directly parallels the increase in cigarette use by both men and women over the last 70 years, with a lag time of about 25 years. In other words, about 25 years after a decline in cigarette use occurs, a decline in the death rate begins to be noticed. Some optimism can be gained from the fact that the lung cancer death rate in men peaked in 1984, and has slowly declined since. This decline appears mostly related to the decreasing use of cigarettes in men in the 1960s and 1970s rather than improvements in diagnosis or therapy. In women the lung cancer death rate has continued to increase although it may have recently reached a plateau. Despite the decline in cigarette smoking in the United States, total cigarette production by U.S. tobacco companies has increased, primarily related to increasing exports to developing countries.
Contents
Risk Factors
About 85% of all lung cancers are attributable to cigarette smoking, making it far and away the predominant risk factor. "Secondhand" cigarette smoke has also been shown to be an important risk factor. For example, there is about 20-30% increased risk of lung cancer in nonsmoking women with spouses who are cigarette smokers. The effects of this exposure on children in the cigarette smoker's home are not yet clearly defined. As many as 4,000 lung cancer deaths each year in the U.S. are felt to be caused by secondhand cigarette smoke.
Cigarettes manufactured in the U.S. today have a significantly lower tar content than cigarettes of 40 years ago. As well, 97% of today's cigarettes are filtered, compared to only 20% in 1955. Both of these changes have been shown to lower risk for lung cancer. These changes have been accompanied by decreased amounts of polycyclic aromatic hydrocarbons (PAHs), but also by increased amounts of carcinogenic tobacco-specific N=nitrosamines (TSNAs) which have been shown to induce adenocarcinoma in lab animals. Mentholated cigarettes do not appear to change lung cancer risk when compared to non-mentholated cigarettes. Lung cancer risks for cigar and pipe smokers are significant, but less than those for cigarette smokers. The reasons for this are generally felt to be the decreased frequency of smoking and decreased depth of inhalation in cigar and pipe smokers compared to cigarette smokers.
Cigarette smokers who stop smoking reduce their risk of lung cancer. In ex-smokers who remain cigarette-free for at least 15-20 years, the risk of lung cancer may approach or equal that of persons who have never smoked. There is some research that suggests that even if a smoker quits smoking for an extended period of time and then restarts, their lung cancer risk may be less than the person who had not at least "temporarily quit".
Various other risk factors also exist for lung cancer. Some of these include significant exposures to asbestos, other silicas, and higher levels of radon. The lung cancer risk associated with exposures to the lower levels of radon that persons may experience in their homes remains controversial. To this point research regarding electromagnetic fields has not shown a significant or consistent association with an increased risk for lung cancer.
The role different dietary factors play in increasing or decreasing one's risk for lung cancer has been the subject of ongoing research. While beta-carotene and vitamin E were once thought to decrease one's risk for lung cancer, current research no longer supports a significant protective effect for either. Other research suggests that vitamin C and selenium may have a protective effect for lung cancer, although eating a diet rich in fruits and vegetables appears to have even a stronger protective effect. Higher intake of fats and alcohol actually increase one's risks for lung cancer.
Studies of families with more than one member having lung cancer suggest that while there likely is at least some genetic predisposition, "shared exposures" may play at least as large a role. Better understanding of the complicated genetics and biological markers of lung cancer will allow for better insight into answers to this question.
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Types & Prognosis
While there are other kinds of lung cancer, by far the most common are termed bronchogenic carcinomas. Within this category there are two main types: small cell and non-small cell lung cancer. This arbitrary division is primarily because of differences in the extent of spread of the cancer at initial presentation and thus differences in treatment. Initial symptoms of lung cancer include otherwise unexplained cough (including bloody cough), breathlessness, or chest pain (usually one-sided). Partly because lung cancer often has no symptoms at all for months to years before it is discovered, the survival rate for lung cancer remains poor. Currently only about 1 person in 7 with newly diagnosed lung cancer (all cell types) is alive 5 years later. This varies slightly with sex (better survival for women), race, age, and the specific cell type of the lung cancer. Small cell lung cancer has a poor overall prognosis, with only about 6% of patients surviving at 5 years. Non-small cell lung cancer often has a better prognosis, but this again depends upon the extent of spread of the disease at the time it is initially diagnosed. If non-small cell lung cancer appears to be confined to one lobe of one lung, and that lobe is surgically removed, the 5-year survival rate may be up to 80%. Unfortunately, this subset of patients comprises only about 15% of newly diagnosed lung cancer patients.
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Screening Tests
While screening tests have allowed for earlier diagnosis and better cure rates for other types of cancers (e.g., routine mammograms for breast cancer), screening tests for lung cancer have been of limited value in the past. These tests have primarily included yearly chest x-rays or sputum analyses. When large groups of patients have been screened with these tests, more lung cancers were detected earlier, but this did not appear to improve the rate of cure or likelihood of survival. More recently, spiral CT scans of the chest have been used to screen for lung cancer in persons at higher-risk, primarily heavy cigarette smokers. Spiral CT scans are more sensitive than regular chest x-rays in the early detection of lung cancer. Initial research has demonstrated earlier detection of lung cancer in the high-risk population studied with spiral CT scans, but how this will impact the screening of lung cancer in the general population remains to be seen. Another "newer" imaging study, Positron Emission Tomography (PET), may be of value in certain patients with possible or proven lung cancer, especially in determining the extent to which the cancer has spread.
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Treatment
Treatment options for lung cancer include surgical resection, radiation therapy, and palliative treatment of specific complications of the tumor. In non-small cell lung cancer surgical resection is generally the only treatment that is curative. However, even if the initial evaluation suggests that surgical resection would be curative, overall survival at 5 years is only about 70%. Radiation therapy can often slow or stall tumor growth or even cause the tumor to shrink in size.
Unfortunately, it is very rare for radiation therapy to cure lung cancer. Chemotherapy can sometimes prolong the life of patients with lung cancer, especially when used in combination with other treatment like radiation therapy. Small cell lung cancer metastasizes early to lymph nodes and blood vessels, and, therefore, is usually not amendable to surgical resection for attempted cure. Chemotherapy is the mainstay of treatment, often with a favorable short-term response (e.g., shrinkage of the tumor). Better education of children and teens about the harmful effects of cigarette smoking remains the most important preventative measure for decreasing the incidence of lung cancer. The improved success of some smoking cessation programs also gives us reasons for optimism in the battle against this terrible disease.
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