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close this bookWIT's World Ecology Report - Vol. 08, No. 3 - Critical Issues in Health and the Environment (WIT, 1996, 16 pages)
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View the documentPoint of View

Cancer and the Human Environment

Harri Vainio, M.D., Chief, Unit of Carcinogen Identification and Evaluation, International Agency for Research on Cancer, Lyon, France.

Cancer is rising in importance on economic as well as health agendas throughout the world. The second leading cause of death in most of the industrialized world, it is already first in some places. Developing countries appear to be launched on a cancer epidemic curve similar to that of developed countries. More than 6 million new cases of cancer occur worldwide each year, distributed almost evenly between the economically developed and the developing nations. Cancer accounts for a fifth of all deaths in industrialized countries and for a tenth in developing ones. The major proportion of the increase in cancer will take place in the developing countries as their populations grow and age. The incidence of cancer is strongly dependent on the age distribution of the population because the risk of getting cancer increases greatly with age. In men, cancer is three times more likely to occur at age 80 that at age 60 and 25 times more likely at 60 than at 40.

The risks of some types of cancer have declined substantially in the developed world, yet, incidences of cancer associated with environmental factors are growing. These diseases which include cancer of the lung, breast, prostate, colon and rectum have increased in countries where smoking, unhealthy dietary habits including alcohol consumption, and exposure to carcinogenic chemicals have become more common. The incidences of some cancers differ between developed and developing countries. Cancer of the cervix, the oral and pharyngeal cavity, esophagus, and liver are more common in developing countries, while lung, female breast, colorectal, and prostate cancer occur more commonly in industrialized societies. As countries make the transition from economically evolving to developed, the incidence pattern of different types of cancer is likely to change.

It is highly likely that the number of cancer cases will increase world wide in the coming decades, and the majority of all cancer deaths will occur in the developing parts of the world. More than two-thirds of all cancers are considered to be of environmental origin increasingly caused by human activity and resulting from exposure to carcinogenic agents. This observation is supported by studies of geographical variation in cancer risk, studies in migrant populations, change in cancer incidence over time, and determination of specific causal factors for human cancer. A major source of the data that point to environmental causes of cancer is the observation of the profound variation in cancer incidence between different human populations, even when differences in the age structure are taken into account. Studies have shown that in some situations, migrant populations tend to develop a cancer pattern resembling that of the population in the area to which they migrate. Data collected by the International Agency for Research on Cancer (IARC) from a large number of cancer registries illustrate the international variation in cancer incidence. For men, the probability of getting cancer in the period from birth to age 75 ranges from 12% in India to more than 30% in the US, France, and Switzerland. In women, the probability ranges from 12% in India to more than 25% (white women) in the US. Thus, regardless, of population, a considerable proportion of people get cancer. In a population with a long life expectancy, about one in four people will develop cancer, and nearly one in five will die of the disease.

A much stronger variability in cancer incidence appears when considering individual types of cancer than when considering cancer overall. Stomach cancer incidence in men varies greatly between Japan and the US. A high incidence of this cancer is also seen in Latin America and Eastern Europe. Liver cancer occurs more commonly in Chinese populations than elsewhere, while cancer of the cervix occurs more often in Colombian women than in other populations. Colorectal cancer and breast cancer are most prevalent in affluent European populations, a tendency also seen for prostate cancer, which is even more common among American blacks.

Main Cancer Killers (all countries, 1993)

Trachea, bronchus and lung

1,035,000

Stomach

734,000

Colon and rectum

468,000

Mouth and oropharynx

458,000

Liver

367,000

Female breast

358,000

Oesophagus

328,000

Cervix

235,000

Lymphoma

221,000

Pancreas

214,000

Leukaemia

207,000

Prostate

182,000

Bladder

135,000

Ovary

123,000

Uterus

64,000

Skin

37,000

SOURCE: The World Health Report 1995


Worldwide, lung cancer is now the most frequently occurring malignancy. It is a common disease in men in nearly all populations, but primarily in economically developed regions and among the Chinese. In the United Kingdom, about 115 deaths occur per 100,000 annually. Lung cancer rates are lowest where smoking is less common, such as Costa Rica (6 per 100,000) and Israel (25 per 100,000). Although the great majority of lung cancer cases are caused by tobacco smoking, occupational exposure to carcinogenic compounds increases the risk of cancer. The most important occupational carcinogen worldwide is asbestos fibers. Exposure occurs in asbestos mining, ship building and construction work. Other occupational carcinogens include exposure to radon, nickel and chromates. Air pollution has been strongly associated with lung cancer. Several epidemiological studies suggest a link between lung cancer and air pollution from the observation of an urban-rural gradient in lung cancer risk. In a case-control study from a heavily polluted area of Poland, it was estimated that 4.3% of the lung cancers in men and 10.5% of those in women were attributable to air pollution. A recent study carried out among nonsmokers in California indicated that the risk of cancer increased concurrently with long-term ambient concentrations of total suspended particles.

Although the cancer-control strategies in North America and Western Europe emphasize high technology treatment, on a global scale, prevention is the preferred strategy. Most potential cases of cancer could be avoided by applying existing knowledge, for example, stopping tobacco use, reducing alcohol consumption, decreasing occupational and environmental exposure to carcinogens, and through hepatitis B vaccination. In Southeast Asian countries such as India, where oral cancer is particularly prevalent, programs to reduce the chewing of tobacco are needed. In sub-Saharan Africa and parts of Asia, liver cancer is one of the most common malignancies, caused mainly by infection with hepatitis B virus and contamination of food with aflatoxins. In Gambia, for example, 80% of the population has been infected with hepatitis B virus by age 15, and 15% to 20% may develop chronic carrier status, which is associated with a highly elevated risk of liver cancer. Hepatitis vaccination is likely to be cost-effective and should form part of cancer-control strategies where hepatitis B virus incidence is high, together with efforts to reduce aflatoxin exposure which results from improper food preservation.

Preventive action to reduce cancer risks based on current knowledge can control the cancers of tomorrow.