Environmental Factors
Summary of Key Points
History of Identification of Human Carcinogens
• The carcinogenic effects of many environmental and occupational agents were first described in humans.
• Beginning in the 20th century with the advent of animal bioassay programs, evidence of carcinogenicity in experimental animals has preceded evidence from epidemiological or case studies in humans.
• Most human cancers probably result from the interaction of several or more carcinogenic influences (often unidentified) along with intrinsic factors (e.g., inherited genes, hormones, and immune status).
Role of Environmental Agents in the Etiology of Human Cancer
• Although the causes of many human cancers remain unidentified, cumulative data support the opinion that environmental or dietary agents are the principal cause of human cancers.
• Cigarette smoking could be responsible for 25% of all cancers in the United States.
• Chemical carcinogens include aromatic amines, benzene, aflatoxins, tobacco chemicals, and chemotherapeutic agents.
• Radiation carcinogens include ultraviolet radiation, ionizing radiation, and radon.
• A number of metal carcinogens have been identified, including arsenic, nickel, cadmium, and chromates. These carcinogens have been associated largely with occupational exposures.
• Fibers (e.g., asbestos and silica) and dusts are well established as etiologic agents in lung cancers and mesothelioma.
