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Biomedical subjects

J Wilbourn

Publications and source records attributed to J Wilbourn.

At least 19 recordsLinked to original sources
PubMed1998

An IARC evaluation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans as risk factors in human carcinogenesis.

The International Agency for Research on Cancer (IARC) Monographs program reevaluated polychlorinated dibenzo-p-dioxins and evaluated polychlorinated dibenzofurans as possible carcinogenic hazards to humans in February 1997, using the most recent epidemiologic data on exposed human populations, experimental carcinogenicity bioassays in laboratory animals, and supporting evidence on relevant mechanisms of carcinogenesis. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was evaluated as carcinogenic to humans (IARC group 1 classification) on the basis of limited evidence of carcinogenicity to humans derived from follow-up of workers who had been heavily exposed in industrial accidents and sufficient evidence of carcinogenicity in experimental animals. The evaluation also considered the following supporting evidence: TCDD is a multisite carcinogen in experimental animals and has been shown by several lines of evidence to act through a mechanism involving the aryl hydrocarbon receptor; this receptor is highly conserved in an evolutionary sense and functions the same way in humans as in experimental animals; tissue concentrations of TCDD are similar in heavily exposed human populations in which an increased overall cancer risk was observed and in exposed rats that developed tumors in carcinogenicity tests. Other polychlorinated dibenzo-p-dioxins, the nonchlorinated dibenzo-p-dioxin, and polychlorinated dibenzofurans were evaluated as not classifiable as to their carcinogenicity to humans (group 3).

Animals↗
PubMed1995

Current Perspectives on Occupational Cancer Risks.

On the basis of the International Agency for Research on Cancer's evaluations of occupational exposures, 22 occupational agents are classified as human carcinogens and an additional 22 agents as probable human carcinogens. In addition, evidence of increased risk of cancer was associated with particular industries and occupations, although no specific agents could be identified as etiologic factors. The main problem in the construction and interpretation of such lists is the lack of detailed qualitative and quantitative knowledge about exposures to known or suspected carcinogens. The recent examples of recognized occupational carcinogens, such as cadmium, beryllium, and ethylene oxide, stress the importance of the refinement in the methods for exposure assessment and for statistical analysis on the one hand and the potential benefits from the application of biomarkers of exposure and early effect on the other hand. Other trends that may be identified include the increasing practice of multicentric studies and investigations of exposures relevant to white collar workers and women. Finally, there is a need for investigation of occupational cancer risks in developing countries.

Journal Article↗
PubMed1993

Cancer etiology: agents causally associated with human cancer.

Cancer is a multifactorial and multistage process, the exact mechanisms of which are still only partially known. However, even in the absence of a complete understanding of the process of carcinogenesis, we have been able to identify several factors which modify the risk of tumour development in humans. These include both endogenous and environmental factors, ranging from exposure to a single identified chemical to the occupations we follow in order to make our living. Cancer prevention strategies may differ in different parts of the world. In Europe, lung cancer is responsible for about one fourth of all cancer deaths and most of it could be prevented by eliminating tobacco smoking. Other exposures that can be controlled include occupational exposures to agents known to cause cancer at sites such as lung, bladder, paranasal sinuses, leukaemia, lymphoma and liver, as well as exposure to sunlight, known to be associated with both non-melanocytic and melanocytic skin cancer. Liver cancer is a common cancer in other regions of the world where hepatitis B virus (HBV) infection is endemic; in these areas, fungal contamination of food is also common. While immunization against HBV may be the method of choice in the long run, reduction of exposure to aflatoxins might be a more useful intermediate goal in primary prevention because of the strong interaction between hepatitis B and aflatoxin exposure on liver cancer risk. To date, few chemical agents have been proved to be of etiological relevance to cancer in humans at sites such as the breast (with the exception of oestrogenic hormones), ovary, colon-rectum and prostate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Occupational cancer in developing and newly industrialized countries.

Cancer is a worldwide public health problem, accounting for an increasing proportion of all deaths. It is the second leading cause of death in most of the industrialised world, and developing countries appear to be launched on a cancer epidemic, similar to that in industrialised countries. In developing countries, most cancer deaths are due to tumours of the stomach, oesophagus, lung, liver and uterine cervix; occupational cancers account for an undetermined number of these cases. Occupationally associated neoplasms may either be related directly to specific exposures within a workplace, e.g., bladder cancer in benzidine-exposed workers, or reflect indirect factors, including socioeconomic status and conditions of life. Asbestos-induced pneumoconiosis is recognised as an occupational disease in many developing countries, whereas asbestos-related malignancies draw less attention. The rising prevalence of cigarette smoking in these countries greatly magnifies the effect of asbestos in inducing lung cancer. Transplantation of industries from developed to developing countries is often accompanied by a reduction in the standard of working conditions. The rising unemployment in developing countries is unlikely to incite workers to claim better conditions.

Animals↗
PubMed1992

Identification of carcinogens within the IARC monograph program.

Fewer than 50 chemicals, groups of chemicals, or mixtures have been causally linked with cancer in humans. Some 250 chemicals have, however, been found to be carcinogenic to rodents. Carcinogenic risk factors that have been identified for humans occur in clearly quantifiable exposure situations, but epidemiologic information on cancer in humans is missing or inadequate for the great majority of chemicals. Extrapolation of animal data to humans is complicated because long-term carcinogenicity studies on animals are carried out under simplified conditions, whereas humans are exposed to a multitude of exogenous and endogenous agents. Furthermore, the carcinogenic process includes multistage and multifactorial aspects, and human populations are genetically and physiologically heterogeneous. Although the science of carcinogenesis is making rapid progress in terms of understanding some of these processes and interactions, there is still a need to err on the side of safety and accept animal data as a warning signal for possible human effects.

Animals↗
PubMed1992

Human cytogenetic damage as a predictor of cancer risk.

The human cytogenetic assays presently available for biomonitoring are still inadequate for use in routine surveillance procedures and they must be applied with care. Knowledge of the effects of the agents concerned in experimental systems is a prerequisite, and confounding factors should be assessed. Consequently, the methods are useful and informative under carefully selected conditions and can indicate agents and exposures that are capable of causing chromosomal damage in humans, hinting at possible human cancer risk. Established and potential human carcinogens have frequently been shown to induce chromosomal aberrations in humans in vivo. It is also well documented that chromosomal rearrangements play an important role in the development of neoplasia. These combined lines of evidence suggest that structural chromosomal aberration in vivo has advantages over other cytogenetic end-points in predicting potential human cancer risk. Preliminary findings in a prospective follow-up study suggest that subjects with a high percentage of structural chromosomal aberrations but not sister chromatid exchanges may be at elevated risk for cancer.

Chromosomes↗
PubMed1991

Carcinogenicity evaluations and ongoing studies: the IARC databases.

Many thousands of chemicals are produced industrially and many more occur naturally. Information on the toxicology of these chemicals is often minimal or absent. The International Agency for Research on Cancer (IARC) has published evaluations of the carcinogenic risk to humans of over 700 chemicals, groups of chemicals, and complex mixtures as a regular series of monographs. A database has been created containing summaries of all the relevant epidemiological, animal carcinogenicity, and other relevant biological data for each chemical or mixture evaluated. Additional databases have been created for ongoing epidemiological studies of cancer in humans and for long-term carcinogenicity studies in rodents, as well as a database containing information on genotoxic and related effects of chemicals. Some of these databases have been published in print form. IARC now plans to publish them electronically, together with other databases, in the form of a CDROM (compact disk, read-only memory). The objective will be to make the entire IARC database of cancer information as widely available as possible in an integrated format conducive to efficient and combined exploitation of all the component databases.

Animals↗
PubMed1989

Human carcinogens so far identified.

The massive exploitation of natural resources, of which tobacco and asbestos are two conspicuous, though very different examples, and the synthesis of industrial chemicals have generated new hazards and new carcinogens which have been added to older ones. The majority of the over 50 agents that have been firmly identified so far as being human carcinogens belong to the relatively new hazards, that is environmental chemicals or chemical mixtures to which humans have been exposed only during the last century and a half. They are of more importance for cancer occurring in men than in women, and there is no evidence so far that they are related to cancers occurring at some of the most common target sites in either sex. It would be mistaken to believe that complete cancer prevention could be achieved solely by controlling these new, or relatively new, carcinogenic agents, but it would be similarly wrong to deny the importance of trying to control them and of continuing to do so. The experimental approach for the identification of carcinogens has an irreplaceable role to play in preventing the dispersal into our environment of new hazards and in identifying among the chemicals already in use, those that are carcinogenic. That a closer integration between the epidemiological and the experimental approaches may succeed in substantially reducing the size of the unknown region within the spectrum of cancer-causing factors, is today's hope that awaits confirmation. At the same time, advances in the understanding of the mechanisms underlying the different steps of the process leading to the clinical manifestation of cancer may help in the uncovering of agents and risk factors that the approaches used, at least in the way they have been used until now, may not have been apt to identify.

Animals↗
PubMed1986

Response of experimental animals to human carcinogens: an analysis based upon the IARC Monographs programme.

Only the results of epidemiological studies can be used to establish a causal relationship between an exposure to an agent and human cancer; however, such studies often cannot be carried out due to limitations of population or latent period or to the presence of mixed exposures. It is essential, therefore, that the validity be established of extrapolating to humans the results obtained from long-term carcinogenicity tests in animals. The responses of experimental animals to known and suspected human carcinogens, as evaluated in the IARC Monographs series, were analysed as an indication of the sensitivity of animal tests for predicting human carcinogens. Although the response was high - 84% - it would have been even higher had all the compounds been adequately tested experimentally. An additional finding was that for many exposures causally related to human cancer, there is a target organ in common between humans and at least one animal species, despite many inherent physiological differences. These findings show clearly the importance of experimental carcinogenicity studies in the primary prevention of cancer.

Animals↗
PubMed1985

Data on the carcinogenicity of chemicals in the IARC Monographs programme.

Data were extracted from IARC Monographs volumes 1-38 on chemicals and exposures for which some data on carcinogenicity in humans, or sufficient evidence of carcinogenicity in experimental animals existed. In all, 288 chemicals, industrial processes and complex mixtures fulfilled these criteria. For 30 chemicals or mixtures of chemicals, and nine industrial processes, there was sufficient evidence of carcinogenicity in humans; and for 63 chemicals and mixtures of chemicals and for five industrial processes, there was evidence that these exposures were probably carcinogenic to humans. For 61 chemicals or groups of chemicals and six industrial processes or occupations, no evaluation of carcinogenicity to humans could be made. For 115 chemicals there is sufficient evidence of carcinogenicity to experimental animals, but no epidemiological data are available. Publications not earlier referred to on the carcinogenicity of these chemicals and exposures were found for approximately 70. A call is made for further information on these exposures with a view to updating the IARC Monographs.

Animals↗
PubMed1984

Target organs for carcinogenicity of chemicals and industrial exposures in humans: a review of results in the IARC monographs on the evaluation of the carcinogenic risk of chemicals to humans.

Epidemiological observations indicate that cancers affecting different organs and systems in humans have different causes. At the descriptive level, cancer incidence and mortality rates exhibit patterns of geographic and temporal variation which are distinct and separate for each cancer site and even, at a given site, for different histological types (for instance, increasing squamous cell carcinoma of the lung and decreasing stomach cancer in most developed countries in recent decades). The existence of these distinct patterns in itself indicates that different causes are at the origin of cancers at different sites. Hence, it is of scientific and practical importance not only to identify agents that are carcinogenic to humans but also to specify as definitely as possible the target organ(s) of their action. This is done in the present review of results in the International Agency for Research on Cancer Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans.

Bibliographies as Topic↗