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1603
Environmental Causes of Cancer among Native
Americans
Nathaniel Cobb, M.D.
Cancer Prevention and Control Program, Indian
Health Service, Albuquerque, New Mexico.
Age-adjusted mortality from cancer is steadily increasing among Native Americans,
raising concern about environmental causes. Toxic waste dumps, mining activities,
paper mills, military activities, agricultural chemicals, and urban pollution are
common sources of carcinogen exposure on reservations and among the urban
poor. Despite documented hazards, we do not see a pattern of cancer excess that
might result if Native Americans were exposed to these carcinogens more than
o t h e r h e r i c a n s . Abuse of tobacco can be shown to be the most important contributor to cancer mortality among Native Americans. Although there are good reasons
for environmental regulation and clean-up, the most cost-effective method of cancer prevention is tobacco control. Cancer 1996; 781603-6.
0 1996 American Cancer Society.
KEYWORDS neoplasms, environmental pollution, North American Indians, tobacco.
t the turn of the century, cancer was a rare disease among Native
mericans.' This might be attributed to a rural life with little exposure to industrial pollution, a healthy diet of home-grown fruits and
vegetables and wild game, limited use of tobacco, and a tendency to
die young from infectious diseases and injuries. Native Americans
still enjoy some advantage over other groups in the United States,
with age-adjusted cancer incidence and mortality one third less than
the rate for all races combined.' Unfortunately, cancer incidence
seems to be steadily increasing among American Indian and Alaska
Native population^,^ and there is growing concern in native communities that environmental exposures may be the cause. Paper mills
pollute the water with dioxin, while mining and smelting activities
may cause exposure to arsenic, lead, radioactive materials, and air
pollution. Toxic waste dumps pollute water and soil with a variety of
poisons. Jobs in mining and industry can be a source of exposure to
dangerous chemicals, mineral dust, and radon gas. People who work
and live in agricultural areas may be exposed to pesticides and herbicides. Many urban Indians live in poverty, which may be associated
with increased exposure to air pollution, lead, and other hazardous
materials. Inadequate housing can be a cause of exposure to vaporized chemicals such as formaldehyde as well as smoke and fumes
from cooking and heating sources. In recognition of the hazards faced
by minority populations and the poor, President Clinton recently
signed an executive order mandating federal actions to address environmental j ~ s t i c e . ~
The food we eat can be an important source of hazardous exposure and can provide protection from cancer as well. Fish, wild game,
and the fat of sea mammals, which are an important part of the diet
of many Native groups, have been shown to contain pesticide resi-
A,
Presented at the Native American Cancer Conference Ill: Risk Factors, Outreach and Intervention Strategies, Seattle, Washington, June 1619, 1995.
Address for reprints: Nathaniel Cobb, M.D., Director, Cancer Prevention and Control Program,
Indian Health Service, 5300 Homestead Road
NE, Albuquerque, NM 87110.
The opinions expressed in this paper are those
of the author and do not necessarily reflect the
views of the Indian Health Service.
Received May 31, 1996; accepted June 18,
1996.
iij
1996 American Cancer Society
1604
CANCER Supplement October 1, 1996 / Volume 78 / Number 7
dues, PCBs, and heavy metals.' Radioactive isotopes
from nuclear testing may be concentrated in caribou
and other wild food sources.6 The traditional diet of
corn, beans, squash, and game has been largely replaced by processed meats and foods that are higher
in fat and lower in fiber and antioxidants. A high-fat
diet is suspected of contributing to cancer of the
breast, colon, and prostate, whereas antioxidants and
other naturally occurring substances in fresh fruits and
vegetables may prevent a variety of cancers. In parts
of the world where the standard diet is low in fat and
high in fiber, colon cancer is very rare.
Personal or life style exposures, such as the abuse
of tobacco and alcohol. are important causes of cancer
among Native Americans. In the Southwest, where
smoking rates have been very low, lung cancer is extremely rare except among uranium miners.' In other
parts of the United States, however, more than 45%
of Native American persons smoke or chew tobacco.*
Cigarette smoking is the cause of most lung cancer
deaths and contributes to cancer of the larynx, bladder, pancreas, stomach, kidney, and cervix. Smokeless
tobacco use can cause cancer of the mouth. Alcohol
acts with tobacco and other risk factors to increase
the risk of cancer of the throat, liver, and pancreas.
How much cancer mortality is actually caused by
environmental pollution? Which exposures should we
worry about the most? It is rather difficult to reach a
realistic estimate of the proportion of cancers caused
by ambient or industrial exposures. In an important
and widely quoted work, Doll and Pet0 estimate that
environmental exposures play a significant role in 7080% of cancer cases in the United Statesg This figure,
however, includes life style exposures such as diet,
tobacco, and alcohol use. They estimate that only 15% of all cancers are caused by pollution and industrial products. How do we protect ourselves from exposure to these cancer-causing agents? The prevention of disease from personal exposures is usually
based in the health system, through education and
medical intervention, whereas control of ambient environmental exposures is usually the responsibility of
engineers and sanitarians in an environment department. Many tribes have active environmental protection agencies that, with assistance from the U.S. Environmental Protection Agency, Agency for Toxic Substances, and Disease Registry (among others), are
actively trying to clean up some of these hazards.
These tribes must establish priorities for their limited
funds; environmental clean-up is often extremely expensive.
Many tribes ask whether the cancers they are experiencing were caused by environmental pollution.
Table 1 lists some known carcinogens and the cancers
TABLE 1
Some Carcinogens and Associated Cancer Site
Carcinogen
Cancer site
Alcohol
Arsenic
Asbestos
Benzene
Ionizing radiation
Nickel dust
Polycyclic hydrocarbons
Tobacco
Liver, esophagus, mouth, pharynx, larynx
Lung, skin
Lung, pleura, peritoneum, pericardium
Acute myelocytic leukemia
Lung, leukemia, breast, brain, thyroid, other organs
Lung, nasal sinuses
Lung, scrotum, skin
Lung, mouth, pharynx, larynx, esophagus,
pancreas, bladder, kidney, renal pelvis, cervix
Angiosarcoma of liver
~~~
Vinvl chloride
they cause. If American Indians and Alaska Natives
were being exposed to chemicals and radioactive materials at higher rates than other U.S. races, we would
expect to see that reflected in higher rates of leukemia,
breast cancer, lung cancer, lymphoma, and brain and
thyroid cancer. This is not the pattern of cancers we
see, however. Table 2 lists the top 11 causes of cancer
mortality among Native Americans. At the top of the
list is lung cancer, which is also the largest cause of
cancer death for all U.S. races. The lung is one of the
most sensitive organs to carcinogenic agents; lung
cancer has been demonstrated to follow exposure to
asbestos, arsenic, diesel exhaust, radon, coal tar products, and many industrial chemicals and heavy metals.
Can we blame the large number of lung cancer deaths
on environmental pollution? Probably not; it has been
demonstrated that 87% of all lung cancer cases in the
US. are caused by cigarette smoking," and smoking
rates among American Indians and Alaska Natives are
high enough to explain the current lung cancer rate.
For comparison, U.S. adult male smoking rates peaked
in 1964 at nearly 50% and have been dropping steadily
since then. Twenty-five years later, the lung cancer
death rate for that group has leveled off at approximately 74 deaths per 100,000 each year." We do not
have good information on Native American smoking
rates from 25 years ago, but the 1991 smoking rates
for Native American males ranged from 20% in the
Southwest to as high as 70% in the Northern Plains
and Alaska; the age-adjusted lung cancer death rate
was only 40 per 100,000 and rising steadily." The nonsmoking Southwest tribes have been heavily exposed
to uranium mining and milling and the residual mine
and mill tailings, yet the lung cancer death rate in
northeastern Arizona is 7.6 per 100,000, less than one
sixth of the US. all-races rate. Although Southwestern
tribes have maintained low lung cancer rates for some
time, there is evidence that smoking rates are increasing rapidly among the young. Unfortunately, based on
Environmental Causes of CancerKobb
TABLE 3
Costs of Prevention
TABLE 2
Cancer Mortality Among American Indians and Alaska
Natives, 1984-88
Cancer site
1. Lung and bronchus
2. Colon and rectum
3. Stomach
4. Breast
5. Pancreas
6. Prostate
7 . Gallbladderlother biljary
8. All leukemias
9. Cervixuteri
10. Kidney
11. Liver 81 intrahepatic ducts
No. of deaths
(5 years)
510
175
162
134
128
123
99
94
89
82
81
1605
Ratea
US rate'
32.7
11.2
9.9
8.4
8.3
7.7
5.1
4.4
47.1
20.1
5.1
5.1
5.5
1.7
3.3
2.6
5.0
15.3
8.4
9.1
0.8
6.4
Does not include Oklahoma, Portland, and California Areas because of known inaccuracies of racial
idenrificatioii in those areas.
Bold = Greater than IJS rate.
* /\I1 rates per 100,000 population, agti-adiusted to 1970 US population.
current trends in smoking behavior, we expect to see
rising lung cancer rates among all Native American
groups well into the next decade.
Of the other top cancers on the list, age-adjusted
Native American death rates exceed U.S. rates for cancer of the stomach, gallbladder, cervix, kidney, and
liver. Could any of these be related to excessive exposure to environmental pollution? We will go through
the list.
Stomach cancer is generally found in societies in
which access to refrigeration is a problem and in
which foods are preserved by salting, smoking, and
pickling. It may also be influenced by chronic H.
pylori infection. A hundred years ago stomach cancer was far more common than lung cancer in the
United States, but the incidence has been steadily
dropping since then. If this cancer was caused by
environmental pollution, we should expect to see a
steady increase.
Gallbladder cancer is much higher in Native Americans than other races, probably because of the same
genetic factors that cause the high prevalence of gallstone~.'~
Cervical cancer is most commonly caused by infection with human papillomavirus. Smoking has been
found to be a minor contributor as well.14
Kidney cancer is also related to smoking, genetic
factors, and possibly environmental exposures.
The excess of liver cancer is probably caused by high
rates of hepatitis B infection'5 and cirrhosis from
chronic alcohol abuse.
Intervention
Cost (per life-year saved)
Smoking cessation advice
Alcohol safety programs for drunk drivers
Mammography every 3 years, age 50-65
Annual mammography age 55-64
Annual Pap screening women >20
Radon remediation in homes:
>21 pCilL
>a pCi/L
>4 pCilL (EPA recominended)
Radionuclide emission control during
disposal of uranium mill tailings piles
Benzene emission control at bulk gasoline
terminals
$<O-9,79ga
$20,968
$2,706
$108,401
$50,348-1,477,24gb
$6.107
$34,990
$141,301
$39,589,443
$155,467,742
$<O means an overall cost savings.
Ranee of values are from different sources.
It seems that much of the excess cancer among
Native Americans can be explained by genetic, infectious, and life style influences. The fact that Native
American cancer rates were so extraordinarily low until quite recently seems to be evidence for a life style
and environment that is (or was) relatively free from
harmful exposures. One current measure of this is that
only 18% of Native Americans live in counties with
significant air pollution, compared with 23% of whites,
25% of African Americans, and 42% of Hispanics.16
This is only small comfort, of course, because we know
that the U.S. population in general is exposed to more
harmful chemicals than are good for us.
The problem of setting priorities remains a difficult one. A recent publication attempted to compare
the costs of prevention for a variety of health and environmental problems." The authors conducted an extensive review of the literature on costs of prevention,
converting cost-effectiveness estimates to a common
measure of "cost per year of life saved." Although the
assumptions used in different studies varied widely,
at least this approach allows us to look at a range of
cost estimates made by different researchers. Table 3
shows some representative costs of life-saving interventions from this article. These numbers should be
used with some caution, as the assumptions made
by different researchers may or may not match your
situation. In a comparison of 587 interventions, the
authors found that the median medical intervention
cost $19,000 per life-year saved, the median for injury
reduction cost $48,000 per life-year, and the median
toxin control cost $2,800,000 per life-year. In contrast,
the simple prevention measure of smoking cessation
advice can result in a net savings, and in the least
1606
CANCER Supplement October 1, 1996 / Volume 78 / Number 7
favorable analysis costs less than half of the median
medical intervention. This article demonstrates that
environmental clean-up and regulation are often extremely costly when calculated on the basis of human
illness prevented.
When considering a multimillion dollar remediation action, we need to ask the following questions.
Does this situation really represent a possible threat
to human health or to the environment? Might the
money be better spent on other interventions that will
have a known positive impact? An example from
Alaska (this is the short version): Some years ago, small
amounts of radionuclide tracers were placed in the
ground in northwestern Alaska to study the movement
of radioactivity through permafrost. Recent publicity
led to an expensive remediation effort, despite dose
calculations and expert opinions that found no risk to
the population from this radiation source. The same
millions could have been used to provide the Alaska
Native population with comprehensive cancer screening and prevention services, with far more positive
effect on the health of the people.
This is not to say that we should not regulate and
clean up our environmental pollution. Clearly, there
are hazardous materials out there that are causing human illness and death as well as harming plant and
animal ecosystems. Studies of the massive industrial
pollution in Eastern Europe and the former Soviet Republics have demonstrated that human health effects
become evident only after fish, wildlife, and forests
have suffered tremendous damage and the more susceptible species have become extinct. When allocating
our scarce resources, however, we must balance the
cost of various interventions against the good that we
expect to come of each intervention.
In conclusion, the evidence indicates that environmental exposures are not the major source of cancer in the American Indian and Alaska Native populations, but there are certainly many good reasons to
continue to regulate and clean up sources of pollution.
When it comes to preventing cancer, however, the
most cost-effective thing we can do is control the
abuse of tobacco. Achieving a more healthy diet is
probably the next most effective intervention.
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