Perinatal carcinogenesis: biologic curiosity or practical necessity?

Factors that require consideration in extending carcinogen bioassay protocols to include transplacental exposure of rodent subjects are summarized. These include metabolic complexities and biologic problems, such as the differences in fetal susceptibility to lethal, teratogenic, and carcinogenic effects of the same compound at different stages of intrauterine development, and that, with the present limited knowledge of transplacental carcinogenesis, transplacental and neonatal exposure to suspected carcinogens may lead to insoluble problems of interpretation. The view is expressed that agents to which the human fetus may be substantially exposed, including drugs and food additives, should nevertheless be tested for carcinogenicity by transplacental exposure.