in the Chemical faboratory Edrfed by NORMAN V. STEERE, 1 4 0 Melbourne Ave., S.E. Minneapolis, Minn. 5 5 4 1 4
CXXVIII. Occupational Cancer Control and Prevention Winfred F. Malone, Ph.D., Prevention Branch, Division of Cancer Control and Rehabilitation. National Cancer Institute, Bethesda, Maryland
The first occupational cancer was recognized two hundred years ago this year when Percival Pott, in England, reported that the commonly used practice of lowering small boys down chimneys to clean them resulted in a high incidence of scrota1 cancer due to presumably too prolonged exposure to the effects of the soot (Pott, 1775). This was the first epidemiological study relating specific chemicals or reagents to the causation of human cancer. Rehn (1895), among others, reported a high incidence of cancer of the bladder among the aniline dye industry. Since that time, numerous studies have implicated specific substances characteristically associated with specific occupations as being etiologically involved in the causation of cancer. However, it was the 1940's before the importance of epidemiological data and animal data clearly emphasized the importance and potential dangers of chemical substances in the causation of cancer (Hueper, 1964). Passage of the National Cancer Act of 1971 and its approval by the President constituted a new kind of national commitment to conquer cancer. One of the major outcomes of the Act was the creation of the Cancer Control Program with two major objective goals: (1) Preventing as many cancers as possible and (2) improving the health delivery to those who have developed cancer. Cancer research seeks to find means for combating cancer, whereas cancer control is concerned with preventing the occurrence of the disease, minimizing its impact, and reducing the number of cancer deaths. The importance of these activities, and the Cancer Control Program as a whole, is illustrated by the fact that there will be 665,000 new cases of caneer in 1975, with approximately 365,000 dying this year. Lung cancer alone will kill 81,000 persons this year. Lung caneer now accounts for 30.5%of all deaths from caneer among men and a rapidly increasing proportion of all deaths from cancer among women (Cancer Facts, 1975). In a recent American Cancer Society prospective study, Hammond (1972) found that after adjustment for age and smoking, the urban excess of lung cancer occurs only among those men who gave an occupational history of exposure t o A468 / Journal of Chemical Education
dust, fumes, or radiation. This excess appeared to be from 10-15%, which may be taken as an estimate of the probable burden of occupational cancer. The plan of action for cancer control may be visualized as a chain of activities directed a t certain intervention points that are critical t o making progress against cancer: Detection, diagnosis, treatment, and prevention. It is with the prevention aspects that we are particularly concerned here today. The objectives of my presentation are three: 1. T o deuelop awareness of the occupational cancer problem; 2. To inform of sources of materials on known or suspected carcinogens; 3. T o rnotioote action for education and stewardship on your part and the part of chemical industry in the prevention of cancer. The major objectives of an occupational cancer control program involve recognition of the active agent, identifying those a t risk, reducing exposure to the agent through a variety of mechanisms, and finally developing control programs so that goals can be set and programs measured. The objectives of cancer prevention are (1) to systematically advance knowledge of causative factors in the disease and (2) to reduce the occurrence of the disease through application of that knowledge. There are two farms of prevention. One is primary prevention; i.e. avoiding the occurrence of the disease, cessation or abatement of hazardous exposure. The other is secondary prevention, which is early detection and prompt treatment to avoid progression of the disease once i t has started. Recognition of an occupational cancer prahlem has, for the most part, relied on clinical and epidemiological data for initial clues. One may note the way in which the carcinogenicity of bis-chloromethyl ether, asbestos, and vinyl chloride were discovered. There are numerous difficulties, hawever, in conducting epidemiological studies of occupational earcinagenesis. The incuhation oeriod for most cancers is about 20
in exposure with time, incomplete diagnosis of some types of tumors, omission or er-
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rors in reporting occupation in medical histories and occupation on death certificates. and the effects attributable to nonmxupati~nnlagents have made i t difficult tu detect m ~ I mrrrnsrs 1 in cancer risks in specific occupation groups. In addition, technological advances are such as new jobs and exposures come into being and others cease to exist. The results of a given study might well indicate a carcinogenic exposure which had ceased to exist. Manv workers arc otvwnrr of the suhstnnces they handle. T h ~ difft~ult). s may be due tu rhe irrr t h a t s particular agent is referred to by a trade name. Further difficulties result because of many occupational titles that have no specific exposure connotation. Workers change occupations and forget the experience of farmer occupations. Nevertheless, epidemiological studies have been the most effective means of identifying increases in risk in occupational settings (Lilenfeld, 1967).Several examples of recent studies include: (1) The retrospective cohort study of mortality among rubber workers which suggests that they have a risk ratio of three, as compared to the general male population, of dying of leukemia (McMichael, 1974); and (2) the county study conducted by NCI in which 3,056 counties were reviewed for estimates of site specific cancer mortality for the period 1950-1969. Among the findings it was shown that one county in New Jersey leads the Nation in bladder caneer mortality among white men (Hoover, 1975). This excess risk may be due to occupational exposure since 25% of the employed persons in the county work in the chemical industry, mainly concerned with the manufacturing of organic chemicals with a potential for causing bladder tumors; and (3) Epidemiological study conducted several years ago among male chemists in the United States, where there was an excess of deaths from cancers of the lymph organs and pancreas (Li, 1969). This study of members of the American Chemical Society aver a 20-year period also suggests that chemical carcinogens had played a role in the origin of cancer of these sites. A program which provides information on trends in incidence of various forms of cancer and variations in occurrence of cancer among different population groups and in different geographic areas has been recently implemented. This activity known as the SEER Proeram (for Surveillance. ble cause of cancer risks in population groups (SEER, 1975). The reporting system is designed to obtain information on every newly diagnosed case of caneer and every death with cancer among members of a defined population. Currently the program covers a population base which includes approximately 10% of the total U S . population. I t is anticipated that this activ-
ity will, in time, provide much information of importance in controlling cancer. The early work of Bryan, Shimkin (1943), Mantel and others (1961) with recard to auantitation of carcinoeenic respumes and safety levting of potentla1 carcinogenic agcntr led to t h development ~ ol realiut;~nn~mnltesu for chrmreal carcinogenesis. These were essentially a n eatension of chronic toxicity tests. Carcinogenicity from a n experimental viewpoint is demonstrated hy laboratory experiments in which the suspected agents are administered t o test animals. The disciplines applied in the study of chemical carcinogens: 1. Chemistry for the identification, purification, and lahoratory preparation of known and suspected agents. 2. Binchemistry aimed a t elucidation of the metabolic fate of carcinogenic agents. 3. Pathology concerned with evaluating the response of the biological systems. Far the most part, cancers in laboratory animals are essentially the same as human cancers; and, with a single possihle exception, all known human carcinogens are earcinogens in lahoratory animals, Thus, for practical reasons, data derived from use of laboratory animals from toxicity testing are the foundation of efforts to protect the public from the possible harmful effects of chemicals (Newill, 1974). By 1970, about 6,000 chemicals or materials had undergone some form of carcinogenesis bioassay. Hartwell (1951), Shubik (19561, and Peters (1969) have published data on the carcinogenic activity of about 2,500 compounds, and additional summaries will appear soon. I t should he mentioned that some of the data reported earlier were based upon small numbers of animals and therefore only fairly potent carcinogens would have been identified as potentially dangerous. During the last decade, investigators of potential carcinogens have sharpened their bioassay methods, and minimal procedures have been described and utilized for various studies (Maugh, 1974). The proceedings of the 23-25 May 1973 Conference on Carcinogenesis Testing in the Development of New Drugs, edited by Golherg (1974). summarizes the latest views on the design, performance, and interpretation of carcinogenesis testing. The use of in-vitro techniques hoth hiochemical, microbial, and tissue culture for the screening of carcinogenic chemicals is now a distinct possibility (Chemicals Being Tested for Carcinogenicity, 1975). These techniques might have wide applicability in the screening of chemical compounds for carcinogenicity. A number of these techniaues are now heine assessed. At the oresent ttme it C
