Leading Work-Related Diseases and Injuries -- United States

The National Institute for Occupational Safety and Health (NIOSH) has developed a suggested list of the 10 leading work-related diseases and injuries (1). The first two categories, "Occupational Lung Diseases" and "Musculoskeletal Injuries," were recently described (1,2); a discussion of the third category, "Occupational Cancers (Other than Lung)," appears below. OCCUPATIONAL CANCERS (OTHER THAN LUNG)

Cancer kills approximately 430,000 people in the United States annually; the American Cancer Society estimates that some form of cancer will develop in one-fourth of all Americans (3). It is the second leading cause of death and the second leading cause of lost years of potential life in this country (4). A high proportion of all cancers are thought to be caused by "extragenetic" factors, including behaviors (e.g., cigarette smoking, alcohol and drug use, and sexual activities) and toxic environmental exposures in the workplace and the community (5). Evidence for these relationships has been developed principally through epidemiologic and toxicologic studies. The main epidemiologic observations have included: differences in the incidence of cancer between groups with different exposures, changes in the incidence of cancer following migrations, changes in the incidence of cancer over time, etc. Toxicologic studies have led to the identification of specific agents that cause cancer in experimental animals (5).

A possible occupational origin for malignant disease was first recognized when an unusually high frequency of scrotal cancer was observed among London chimney sweeps in 1775 (6). Since then, several types of cancer have been associated with industrial agents or processes (Table 1) (7). Numerous other occupational agents--such as beryllium, cadmium, ethylene oxide, phenoxy-acetic acids, and chlorophenols--or processes--such as newsprint pressroom work--are suspected of being carcinogenic and are under investigation by NIOSH.

Although general agreement exists concerning the overall incidence of cancer, considerable controversy surrounds the proportion of cancer cases attributable to occupational exposures. Several characteristics of cancer contribute to the difficulty in making such estimates:

1. Latency in the development of cancer. Occupational cancer usually becomes evident long after initial exposure to the carcinogen; this interval may vary from 5 years to more than 40 years (9), making it difficult to characterize important exposures long past.

2. Influence of exposures to multiple carcinogens. Cancer victims may have been occupationally exposed to many carcinogens; interaction of these agents or interactions between them and other factors may greatly increase the risk of cancer (10).

3. Influence of behavioral factors. Cigarette smoking, alcohol drinking, and dietary habits also influence the development of cancer (11). Moreover, these factors--especially cigarette smoking--interact with chemical and physical agents in the working environment to increase the risk of cancer (12); e.g., exposure to asbestos interacts with cigarette smoking to greatly increase the risk of lung cancer. In addition, problems with the documentation of cancer and the

nature and extent of etiologic exposures obscure important epidemiologic associations:

1. Errors in diagnosis and classification of cancer. Unusual neoplasms are often misdiagnosed; even correct diagnoses may be improperly categorized according to the International Classification of Diseases (ICD); an example is mesothelioma (10).

2. Lack of meaningful occupational histories. In only a few states is information collected on the work histories of cancer victims; hence, for many cases, crucial associations with occupational carcinogens are not apparent.

3. Difficulty in assessing exposures quantitatively. Precise measurements of levels and duration of exposures have not generally been available (13). Consequently, the ability to delineate dose-response relationships has been very limited.

4. The frequency of specific types of cancers. The occupational etiology of a very rare cancer due to a specific agent (e.g., hemangiosarcoma of the liver due to vinyl chloride) is much more readily documented than the occupational etiology of a cancer type potentially caused by several factors (e.g., lung cancer associated with exposure to chromates).

5. The "dilution factor." Highly significant differences in the rates of cancer among small subgroups of a population may be overlooked because these rates affect the overall rate for cancer in the larger study population only slightly, if at all (8). Despite these difficulties, various attempts have been made to

estimate the proportion of cancers related to occupation. These estimates span a broad range, from less than 4% (5,14) to more than 20% (15). While these estimates are obviously imprecise, little doubt remains that occupational factors are significantly related to an increased risk of cancer. Moreover, in specific groups of workers exposed to specific carcinogens, the proportion who ultimately develop occupational cancer may be large. Of one group of workers distilling beta-naphthylamine who had more than 5 years of exposure, all reportedly developed tumors of the bladder (17); up to 11% of workers exposed to asbestos may ultimately develop mesothelial tumors (16). Reported by Div of Surveillance, Hazard Evaluations, and Field Studies, NIOSH, CDC.

Editorial Note

Editorial Note: Cancer caused by occupational agents, especially synthetic chemicals, is a problem of human origin, and should, therefore, be preventable. Substitution of noncarcinogens for carcinogens, enforcement of protective standards for exposure, design and application of engineering controls, and use of personal protective equipment by exposed workers are major modes of prevention.

Although it is difficult to predict a trend for the future incidence of occupational cancer, the increased volume and diversity of synthetic chemicals manufactured since World War II (18) raise serious concern about the risks from exposure to these substances. However, improved control technology, governmental regulatory activity to reduce exposures, surveillance of disease and risk factors, and vigilant use of preventive measures will ultimately reduce occupational cancer.

References*

1. CDC. Leading work-related diseases and injuries--United States. MMWR 1983;32(2):24-6, 32.

2. CDC. Leading work-related diseases and injuries--United States. MMWR 1983;32(14):189-91.

3. Silverberg E. Cancer statistics, 1982. CA - Canc J Physicians 1982;32:15-31.

4. CDC. Table V. Years of potential life lost, deaths, and death rates, by cause of death, and estimated number of physician contacts, by principal diagnosis, United States. MMWR 1983;32:411.

5. Doll R, Peto R. The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today. JNCI 1981;66:1191-308.

6. Pott P. Chirurgical observations relative to the cataract, polypus of the nose, the cancer of the scrotum, the different kinds of ruptures and the mortification of the toes and feet. In: National Cancer Institute Monograph No. 10, 1963:7-13.

7. Rutstein DD, Mullan RJ, Frazier TM, Halperin WE, Melius JM, Sestito JP. Sentinel health events (occupational): a basis for physician recognition and public health surveillance. Am J Public Health 1983;73:1054-62.

8. Davis DL, Bridbord K, Schneiderman M. Cancer prevention: assessing causes, exposures, and recent trends in mortality for U.S. males 1968-1978. Teratogen Carcinogen Mutagen 1982;2:105-35.

9. Decoufle P. Occupation. In: Schottenfeld D, Fraumeni JF Jr, eds. Cancer epidemiology and prevention. Philadelphia: WB Saunders, 1982:318-35.

10. Selikoff IJ. Constraints in estimating occupational contributions to current cancer mortality in the United States. In: Peto R, Schneiderman M, eds. Banbury report #9: quantification of occupational cancer. New York: Cold Spring Harbor Laboratory, 1981:3-17.

11. Higginson J. Lifestyle and cancer. Cancer Forum 1981;5:4-14.

12. U.S. Public Health Service: Smoking and Health. A Report of the Surgeon General. PHS Pub. No. 79-50066. Washington, DC: U.S. Department of Health, Education, and Welfare, Public Health Service, Office on Smoking and Health, 1979.

13. Davis DL, Bridbord K, Schneiderman M. Estimating cancer causes: problems in methodology, production, and trends. In: Peto R, Schneiderman M, eds. Banbury report #9: quantification of occupational cancer. New York: Cold Spring Harbor Laboratory, 1981.

14. Higginson J, Muir CS. The role of epidemiology in elucidating the importance of environmental factors in human cancer. Cancer Det Prev 1976; 1:79-105.

15. Department of Health, Education, and Welfare. Estimates of the fraction of cancer in the United States related to occupational

16. Newhouse ML, Berry G. Predictions of mortality from mesothelial tumors in asbestos factory workers. Br J Indus Med 1976;33:147-51.

17. Parkes HG. Identification of carcinogenic hazards from aromatic amine exposure and measures of control. In: Nieburgs HE, ed. Prevention and detection of cancer, part I: prevention. New York: Marcel Dekker Inc., 1978.

18. Davis DL, Magee BH. Cancer and industrial chemical production. Science 1979;206:1356-8. _______________

• Additional references are available on request from the National Institute for Occupational Safety and Health, CDC.

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