Maximum tolerated dose, carcinogen risk

Savolainen, K. M. (1997). The use of maximum tolerated dose in rodent carcinogenicity bioas says and its relevance to human risk assessment. Hum. Exp. Toxicol. 16, 190-192. 

No studies were found in humans regarding the carcinogenic effect of chlorobenzene via inhalation. Since this is the primary route of environmental exposure, additional studies would be useful to assess potential risk to people who may be exposed to low levels of chlorobenzene in air near hazardous waste sites. There was no evidence for carcinogenicity in both sexes of mice or female rats following oral exposure to chlorobenzene. Since the animals were tested at the maximum tolerated dose and a no-effect level for tumors in rats and mice has been determined, additional oral studies are not warranted at this time. 

Extrapolating Rodent Cancer Test Results to Humans. It is prudent to assume that if a chemical is a carcinogen in rats and mice at the maximum tolerated dose (MTD), it is also likely to be a carcinogen in humans the MTD. However, until we understand more about mechanisms, we cannot reliably predict risk to humans at low doses, often hundreds of thousands of times below the dose where an effect is observed in rodents. Thus, quantitative risk assessment is currently not scientifically possible (1.17,20). 

---