Back to Contents

ENVIRONMENT AND CANCER

Levshin B.F., Professor, the Russian Cancer Research Centre.

Different forms of cancer belong to comparatively common pathologies, which are characterised by marked differences in morbidity levels, both spatially and in time. In Russia, more than 400 thousand new cases of malignant tumours are registered annually, relevant global figure reaches about 7 million. Cancer morbidity levels are growing world-wide, in particular, in Russia in 15 years (from 1980 to 1994) numbers of patients with initially diagnosed malignant tumours increased by 28.5%. There are two main causes of growing cancer morbidity and mortality: ageing of population and growing carcinogen loads, including environmental carcinogen loads.

Generalisation of long-term studies in the sphere of cancer aetiology and epidemiology allows us to identify the major underlying causes of these diseases and estimate relative contribution of a given factor or a group of factors into overall incidence of cancer cases.

Causes of cancer:
% of cancer cases, associated with a particular factor

Environmental factors or potential external carcinogens incorporate naturally occurring carcinogens, some artificial carcinogens (products of human activities), environmental contaminants, some occupational exposures, solar and ionising radiation, some fungi and viruses, entering the human body, and nutrition (to some extent, because many chemical compounds enter food products from environmental media), passive smoking.

Generally, environmental factors may substantially affect population cancer morbidity and mortality levels. The above assumption is confirmed by information on changes in cancer morbidity of migrant population groups. Generally, migrants of the second generation and subsequent generations of former migrants have the same cancer morbidity levels as indigenous residents of their destination regions. These facts confirm the decisive role of environmental factors and lifestyle patterns in cancer aetiology.

Chemical carcinogens in the environment belong to the most closely studied group of cancer-inducing factors. According to the International Agency for Research on Cancer, about 60 thousand different chemical compounds are used now world-wide. Assessments of carcinogenic effects were conducted for 800 of them. From the above group, 50 chemical compounds and mixtures have been were proven to have causal links with human cancer, other 196 compounds and mixtures have been assessed as potential human carcinogens.

Chemical carcinogens incorporate domestic and occupational ones, however, some of them might be encountered both in domestic and workplace environments. The list of the most common carcinogens incorporate: asbestos (lung cancer), 2-naphtilamine and benzidine (bladder cancer), shale oil and soot (skin cancer), vynylchloride (liver cancer), wood dust (cancer of the nasal cavity), lead, mercury, cadmium, arsenic, nitrosoamines, polycyclic hydrocarbons, nickel and chromium compounds, pesticides and herbicides.

Some viruses and mould fungi might be also classified as external or environmental carcinogens. For example, some fungi, that damage cultivated crops and food products at storage (grain), generate mycotoxins (including aphlotoxins, than may cause human and animal malignant tumours). Human papilloma virus promotes development of malignant tumours of cervix uteri, Epstein-Barr virus promotes nasopharynx cancer, viruses of hepatitis B and C promote development of liver cancer.

Some compounds demonstrate rather potent carcinogenic effects. For example, exposure to benzidine and 2-naphtiamine may increase risks of bladder cancer in 500 times. However, population risks and loads of these carcinogens are minimal, because people may have contacts with them only at some specialised production facilities, where occupational human contacts with these carcinogens are usually controlled and regulated. At the same time, some other carcinogenic factors, e.g. radon, some viruses and nitrites, that increase cancer risks only in 2-3 times, may have more serious health impacts on a population due to their higher occurrence. Besides that, it is necessary to account for transplacentary effects of some environmental carcinogens.

Roles and impacts of environmental factors may substantially vary in different regions and for different forms of cancer. For example, solar radiation may generate carcinogenic effects only in the case of skin cancer. As a result, in regions with high daily/annual levels of solar radiation, incidence of skin cancer might exceed relevant figures for regions with minimal solar radiation levels in several times. Carcinogenic effects of solar radiation may grow with depletion of the ozone layer, that protects the Earth surface from short-wave UV - the most carcinogenic component of solar spectrum.

A strategy for population protection from external/environmental carcinogens should be based on identification and elimination of these factors and implementation of relevant environmental protection measures. It is necessary to implement the following actions:

• monitoring of carcinogens in environmental media with application of physical, chemical and biological techniques;

• control of carcinogens in the environment: elimination, control and regulation of all known carcinogenic agents or impacts in household and workplace environments;

• development of rational technologies, allowing to eliminate or reduce carcinogenic impacts on human health in household and workplace environments to maximal possible extent;

• sanitary and toxicity testing of all new compounds and preparations to identify their potential mutagenic and carcinogenic effects;

• environmental, sanitary and cancer-prevention public awareness raising activities.

Environmental protection is one of the most promising and efficient cancer-prevention activities.

Back to Contents