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Lung and
Larynx Cancer
Jay H. Lubin,
Ph.D.*
Primary lung cancer accounts for about 15
percent of all cancer cases (19 percent in males and 11 percent in females) in
the United States; however, because of its high death rate, it accounts for 29
percent of all cancer deathsÑ35 percent in males and 21 percent in females
(Boring et al., 1994). The overall 5-year relative survival rate is only 13
percent (Ries et al., 1994).
Lung cancer remains the leading cause of
cancer death in most countries. Maoris of New Zealand experienced the highest
incidence rate in the world among males, with a world standardized rate of 119.1
per 100,000 (Parkin et al., 1992). U.S. black men were near the highest, with an
incidence rate of 90.0 per 100,000. Low rates were noted for Israel, India, and
Latin American countries.
The worldwide incidence of lung cancer is
substantially lower in females--a difference generally attributed to lighter
tobacco consumption by women, although other factors may play a role. For
example, high levels of indoor and outdoor air pollution have been postulated as
an important contributor to the high rates of lung cancer among females in
China, whose smoking prevalence is relatively low (Blot and Fraumeni, 1992).
In the United States, lung cancer
incidence has risen more sharply in females (4.6 percent annual change) than in
males (0.5 percent annual change) in recent years, reflecting the growing
popularity of cigarette smoking among females over the past several decades (Ries
et al., 1994). Currently, more women die each year from lung cancer than breast
cancer (Boring et al., 1994).
Although overall age-adjusted mortality
rates of lung cancer continue to rise in the United States, rates have begun to
decline for those under the age of 45 (Devesa et al., 1989). The decrease is
greatest among white men, but a decrease among black men and white and black
women has also occurred. If trends continue, overall lung cancer mortality rates
will start to decline among men in the 1990s and among women after the year
2000.
Cigarette smoking is the major cause of
lung cancer. The link was first suspected in the 1920s and 1930s, and today,
after multiple case-control and cohort studies, the overwhelming evidence is
documented in more than 20 reports of the U.S. Surgeon General. Smoking is
currently estimated to cause 85 percent of all lung cancer deaths. Lung cancer
mortality increases with increasing dose, as determined by number of cigarettes
smoked daily, smoking duration, and inhalation patterns. The risk of dying from
lung cancer is 22 times higher among male smokers and 12 times higher among
female smokers than among people who have never smoked (U.S. DHHS, 1990).
Cessation of smoking reduces the risk of
death from lung cancer; after ten years the risk of lung cancer death among
former smokers is about 50 percent of the risk of continuing smokers (U.S. DHHS,
1990). Those who reduce their daily usage and those who smoke filtered, low-tar
cigarettes gain some benefit, although they still have lung cancer risks much
higher than nonsmokers (Lubin et al., 1984).
Environmental tobacco smoke (ETS) has been
determined to increase the risk of lung cancer in nonsmokers. This conclusion,
presented in both the 1986 U.S. Surgeon General's Report (U.S. DHHS 1986) and a
Report of a Committee of the National Academy of Sciences (NAS 1988), was based
on a variety of evidence including more than 20 epidemiologic studies, as well
as laboratory analyses which show the components of sidestream smoke to be
qualitatively similar to mainstream smoke. Evidence suggests that persons
exposed to ETS are subjected to a lung cancer risk equivalent to smoking 0.1 to
1.0 cigarettes per day.
Increased risk of lung cancer has also
been associated with the smoking of pipes and cigars, but at a lower level of
risk than that for cigarettes. This may be due to a less intense pattern of
smoking, with cigar and pipe smokers typically inhaling less deeply and less
frequently.
Radon is an inert gas produced by the
radioactive decay of radium and uranium. While concentrations of these elements
vary widely, they are found everywhere in the crustal rock of the earth. Radon
itself is radioactive and may cause lung cancer. Studies of underground miners
exposed to radon have consistently shown an increased risk of lung cancer with
greater cumulative exposure to radon and its short-lived decay products (Lubin
et al., 1994; NAS, 1988; Samet 1989). The results of these studies, together
with animal studies, suggest that radon exposure is a cause of lung cancer, at
least at levels historically found in mines.
Radon may also enter homes by migrating
from the earth through cracks in the foundation, or through the hole for a sump
pump, or, in rare cases, via private water wells, by dissolving in drinking
water. Although the radon concentration in some homes may reach levels found in
mines, average domestic cumulative lifetime exposure to radon is about 5 to 15
times lower than for miners. Based on miner studies, it has been estimated that
radon may cause 6,000-24,000 lung cancer deaths each year in the United States (Lubin
and Boice, 1989). However, because of uncertainties in using miner-based
results, the precise public health consequences of domestic exposure to radon is
currently an important unresolved issue. Results of ecologic studies and
case-control studies, using either indirect estimates of personal exposure or
direct measurements of indoor radon concentrations, have been mixed in showing
an association between radon level in the home and lung cancer risk (Samet
1989).
Studies of occupational groups have
identified several other respiratory carcinogens, although it is difficult to
assess their overall public health impact. Some of these exposures--such as
radon--may be widespread in the population but at very low levels, while other
exposures may have their greatest impact on subgroups of the population, as with
asbestos exposure among shipyard workers. It should be noted that the
carcinogenic effect of some of these exposures, e.g., asbestos, is enhanced by
tobacco smoke.
Exposure to airborne asbestos appears to
be the largest cancer threat in the workplace, raising the risk of lung cancer
and mesothelioma (a cancer that arises in the lining of the chest cavity, or
mesothelium) as well as asbestosis, a lung disease (Blot and Fraumeni, 1992).
The risk of developing these three diseases is substantially higher for workers
in a number of asbestos industries, including miners and millers, and textile,
insulation, shipyard, and cement workers. Lung cancer is the major
asbestos-related disease, and accounts for death in about 20 percent of some men
exposed to asbestos for long periods of their work life (Selikoff et al., 1979).
Even men who worked for short periods in shipyards during World War II have a
higher risk of developing lung cancer than workers never exposed to asbestos
(Blot et al., 1978; 1980).
Lung cancer is also one of the major
effects of high doses of ionizing radiation. Excesses of lung cancer have been
reported among some patients who received radiation therapy, and among atomic
bomb survivors in Japan (Beebe et al., 1978), where both gamma rays and neutrons
were released.
A number of other occupational agents
contribute to the incidence of lung cancer: mustard gas, chloromethyl ethers,
chromium, nickel, and inorganic arsenic.
Air pollution has been suspected as a
cause of lung cancer, but it has been difficult to establish definite links. Of
special concern are the effects of the byproducts of the combustion of fossil
fuels, most notably polycyclic aromatic hydrocarbons (PAHs). Studies have
suggested that exposure to benzo(a)pyrene may increase lung cancer risk. In both
urban and rural areas of China, exceptionally high levels of indoor air
pollutants from the use of coal for heating and for cooking, along with
cigarette use, have been implicated in the high rate of lung cancer (Mumford et
al., 1987; Xu et al., 1989). Although suggestive, the association of lung cancer
and PAHs has not yet been conclusively demonstrated, as other components of air
pollution may also be carcinogenic.
Finally, there is laboratory evidence of a
protective effect against lung cancer with increased intake of vitamins A (retinol
and precursor carotenes), C, E, selenium, and other micronutrients.
Epidemiologic studies have provided support for some of these associations. The
clearest and most consistent associations occur with the consumption of fresh
fruits and vegetables. Studies show that risk of lung cancer was reduced by as
much as 50 percent among those with the greatest compared to those with the
least consumption of these foods (Blot and Fraumeni, 1992). The precise
component responsible is still uncertain, but most attention has been focused on
carotenoids, particularly beta-carotene.
Approximately 12,500 new cases of cancer
of the larynx, or voicebox, occur each year, 9,800 in males and 2,700 in females
(Boring et al., 1994). It has an incidence pattern similar to that of cancers of
the mouth and throat, occurring more often among men than women and more often
among blacks than among whites. The annual incidence of laryngeal cancer among
U.S. white men is 7.8 cases per 100,000 population, and 1.7 among white women.
Among black men, the annual incidence is 13.0 per 100,000, and 2.7 among black
women (Ries et al., 1994).
In the United States between 1973 and
1991, the incidence of laryngeal cancer declined 0.6 percent annually in white
males, but increased 1.6 percent in white females over the same time. In blacks,
the annual incidence increased in both sexes, 0.9 percent in males and 2.3
percent in females (Ries et al., 1994).
Risk factors for laryngeal cancer include
tobacco, alcohol, asbestos, and nickel and mustard gas exposure. As with cancers
of the lung, mouth, and throat, many cases of laryngeal cancer can be attributed
to cigarette smoking. Cigarette smokers have almost a ten-fold greater risk for
laryngeal cancer than do nonsmokers, and risk increases with increased cigarette
smoking (Wynder et al., 1982). Not only is heavy alcohol consumption a risk
factor, but tobacco and alcohol together appear to act synergistically.
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*
From the Biostatistics Branch, Division of Cancer Etiology, National Cancer
Institute, Bethesda, Maryland
National Cancer Institute
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