Invasiveness of Fibrosarcomata in Mice. ∗

Abstract

It has been shown that the characteristic of invasiveness of chemically induced fibrosarcomas (the presence of discrete nodules in the abdomen derived either by direct extension of the tumor or by the process of metastasis) is partially determined by some new principle found in the host which had been derived from its ancestry and differentially determined by litter sedation (1). These conclusions were based upon observations on 788 mice of 2 descents (Prunt and 2Prunt), which were genetically related to each other (17 generations of inbreeding in common).

In the first analysis of an association between invasiveness of fibrosarcomas and litter seriation (mother's age ?), the data on some of the litters were small and it became necessary to add successive litters 1 + 2, 3 + 4, 5 + 6, 7 + 8, 9 + 10 and 11 + 12, together in order to show smoother trends. There were also slight differences between the sexes and between the 2 descents, which, however, were not statistically significant.

In the present analysis dealing with the same phenomenon, 974 new data were added. The combined data on 1,762 mice are given in Table I, according to litter of origin.

The origin and genetic relationship of the Prunt and 2Prunt descents have already been described(l). All mice were injected with 1 mg of methylcholanthrene dissolved in 0.1 cc of sesame oil at 60 days of age and continued as breeders. The young, however, were discarded shortly after birth. The mice were examined weekly for tumors beginning 2 months following the injection of the carcinogen. The latent period was determined by the appearance of a solid firmly attached progressively growing nodule at the site of the injection.