An alternative animal model for perinatal carcinogenesis.

The differences in developmental biology between marsupials and eutherian animals provide alternative approaches to major problems in perinatal carcinogenesis. The high susceptibility of the neonatal American marsupial, the opossum (Didelphis virginiana), during early postnatal development to oral, chemical induction of dysontogenetic tumors with a close morphologic and biologic resemblance to those in the human suggests that the neonatal marsupial may offer unique opportunities for the study of carcinogenesis during ontogenesis without placental interference and under a maternal influence limited to the constituents of milk and contact with skin secretions. Although there is as yet no experimental data on transplacental tumor induction in the marsupial, several aspects of marsupial gestation, including a primitive yolk sac placenta devoid of implantation and an apparent, partial nutritional autonomy of the developing fetus, imply that the marsupial in utero may, like the marsupial neonate, be more accessible to tumor induction than its eutherian counterpart. The results of preliminary attempts to develop pre- and postnatal life support systems (embryo culture and an artificial marsupium) suggest the feasibility of further reducing maternal influence on the developing marsupial in order to enhance the utility of the model. Currently, the opossum and the marsupial mouse (Sminthopsis macroura) appear to be the marsupials of choice for perinatal carcinogenesis experiments.