The first medical case of occupational cancer was reported in 1775 by Percival Pott, who described scrotal cancer among British chimney sweeps. However, it was not until more than 150 years later that benzo(a)pyrene was identified as the probable causative agent in chimney soot.
A number of other causal associations for occupational cancers were made in the two centuries following Pott's early case report. Among these are lung cancer in uranium miners, sarcoma of the jaw in radium dial painters, bladder cancer in workers exposed to aromatic amines, angiosarcoma of the liver in vinyl chloride workers, lung cancer in workers exposed to bis-chloromethyl ether used in plexiglass manufacture, mesothelioma and lung cancer in workers exposed to asbestos, and leukemia and other hematopoietic cancers in benzene-exposed workers.
The International Agency for Research on Cancer (IARC) is an international agency of the World Health Organization that evaluates the carcinogenicity of chemicals. In the United States, chemicals are evaluated for carcinogenicity by the National Toxicology Program (NTP) of the U.S. Public Health Service, the National Institute for Occupational Safety and Health (NIOSH), and the American Conference of Governmental Industrial Hygienists (ACGIH). In California, the Office of Environmental Health Hazard Assessment (OEHHA) of the California Environmental Protection Agency (Cal-EPA) publishes a list of chemicals known to the State of California to cause cancer.
Because workers are typically exposed to a greater number of carcinogens for longer periods of time than the general population, most chemically-induced cancers have first been identified in occupational environments. The estimate typically found in the scientific literature is that about two to eight percent of all human cancers are of occupational origin, while it has been estimated that 85% of all cancer is caused by environmental chemicals. Indeed, it is a common opinion held by most scientists in the field of carcinogenesis that environmental chemicals contribute significantly to the development of cancer in humans and do so to a much greater extent than any other agents.
Of the hundreds of thousands of chemicals known to man, very few have adequately evaluated to determine their carcinogenicity to man. To date, the International Agency for Research on Cancer (IARC) has only evaluated 782 agents or exposure circumstances for carcinogenicity. So far, IARC has determined 66 chemicals or exposure situations to be carcinogenic to humans, 51 to be probably carcinogenic to humans, and 210 to be possibly carcinogenic to humans. IARC has found the data on 454 of these chemicals to be inadequate to assess carcinogenicity. Of the 782 chemicals and exposure situations listed, only 1 has been found probably not carcinogenic to man.
Workers exposed to carcinogens in a number of occupations are at an increased risk of developing cancer. Among those at increased risk are health care workers, pharmaceutical and laboratory workers, refinery workers, painters, leather workers, rubber workers, furniture makers, and pesticide workers. As chemicals and industrial processes continue to be evaluated, additional causes of cancer are ascertained. The story of chemically-induced cancer has only just begun.