The value and significance of life span and scheduled termination data in long-term toxicity and carcinogenesis studies.

Consideration is given to the age association of lesions, the duration of long-term toxicity and carcinogenesis studies, and to the value and significance of including scheduled termination in such long-term studies. There is now enough evidence that age and cancer are associated. It is argued that the increase in incidence of lesions with age has such disadvantages that extension of the duration of the long-term toxicity and carcinogenicity study beyond 2 years is not warranted in most cases. Incorporation of scheduled termination in long-term studies gives more insight into the biologic behavior of toxic lesions and cancer and may enable one to make a distinction between "incidental" and "fatal" lesions. This distinction may be important for the statistical evaluation of data from chemical carcinogenesis studies.