Can a simple test in bacteria identify cancer-causing chemicals in humans?

Abstract Since the 1950s, US officials have sought to reduce cancer incidence by regulating chemical exposures. However, rodent carcinogenicity tests are lengthy and expensive, making it impractical to identify carcinogens among the tens of thousands of chemicals on the market through animal testing. Introduced in 1973, the quick and inexpensive ‘Ames test’ indicated whether a chemical caused mutations in bacteria, and putatively cancer in humans. In the 1970s and 1980s, scientific societies, international bodies and government agencies launched efforts to validate the Ames test for carcinogenicity. While the Ames test became the most commonly used mutagenicity (or genotoxicity) test, technical determinations of its validity could not resolve policy issues concerning how much predictiveness was required for regulatory action. The availability of new animal carcinogenicity data through the 1980s affected calculations of the predictiveness of the Ames test for carcinogenicity, and criticisms of the rodent bioassay also complicated the interpretation of mutagenicity data. This article documents the challenges of validating even a very successful chemical safety test, while paying attention to how academic scientists, government agencies and international bodies participated (and sometimes competed) in setting regulatory standards.