The occurrence of tumours in F 1 , F 2 , and F 3 descendants of pregnant mice injected with 7,12‐dimethylbenz (A) anthracene

Pregnant MA mice were injected intraperitoneally with 400 micrograms of 7,12‐Dimethylbenz(a)anthracene in olive oil during the last stages of pregnancy. The genetic design of the experiment included the follow‐up of the descendants for three consecutive generations and the cross‐mating between the F 1 descendants of treated mothers with descendants of untreated controls. An increased incidence of tumours was observed in the female F 1 and F 2 descendants and the female F 2f descendants (cross‐mating of F 1 female descendants from a treated mother and male descendants from an untreated control). The tumours were observed in animals dying at a late age which approximately corresponded to the age when spontaneous tumours were observed in control animals. The most frequent types of tumours were the same as observed in the control animals, together with a handful of rarely observed tumours. In the F 1 and F 2 male descendants the tumour incidence was higher than in control animals but the difference was statistically not significant (binomial test). No significant increase in tumour incidence was observed in the F 3 and F 2m descendants (cross‐mating of F 1 male descendants from treated mothers with female descendants from untreated controls). While the mice of F 1 generation were directly exposed to small amounts of the chemical carcinogen via the mothers' milk and excreta, and possibly through the placenta, it seems unlikely that DMBA as such was transmitted to the F 2 descendants.