Abstract

In 1974, an issue of Newsweek entitled ‘What causes cancer?’ suggested that ‘At least 60 per cent, and as much as 90 per cent of human cancer is caused by environmental factors, probably chemicals’. This widely-accepted belief was a factor in establishing the United States National Toxicology Program, through which hundreds of chemicals were subjected to chronic toxicity testing in rodents. The goal was to identify those otherwise ‘unknown’ carcinogens that accounted for a significant proportion of human cancer.