| First Author | Mewissen DJ | Year | 1971 |
| Journal | Fed Proc | Volume | 30 |
| Pages | 341 (Abstr #835) | Mgi Jnum | J:35679 |
| Mgi Id | MGI:4440842 | Citation | Mewissen DJ (1971) Natural tumor incidence in a population of mice as a reference index. Fed Proc 30:341 (Abstr #835) |
| abstractText | Carcinogenic potency of a number of environmental factors (chemicals, radioactive waste) is often assessed from induced tumors in excess of natural or spontaneous incidence. These experiments were aimed to investigating the latter in an inbred strain of mice classically referred to as a relatively tumor free one. A total of 1,324 C57 Black/6 male and female mice were observed throughout their life span. Complete autopsy was performed on all animals and tissue samples from selected organs were obtained for microscopic studies. Spontaneous tumors occurred in more than 70% of mice of both sexes as maximum life span attained 1,200 days under pathogen free conditions. Some animals exhibited up to five histologically different tumors, which suggests that such tumors develop on a competitive basis and are not necessarily lethal to the host. Age specific incidence rates for all tumors fit a linear Gompertzian regression up to 800 days then the trend bends over possibly because tumors arising late in small organs like thyroid and prostate are subsequently missed. These findings give support to the hypothesis of vertically transmitted oncogenes and are compatible with a mechanism involving two interacting components, one of phenotypic expression acting at a constant rate, the second of repression gradually losing strength also at a constant rate throughout life span. Furthermore, they suggest carcinogens are triggering rather than initiating agents. |
