Cancerous ancestry and the incidence of cancer in mice.
Breeding experiments with cancerous mice have been in progress for the last 5 years in the laboratory of the Imperial Cancer Research Fund. The purpose has been the collection of data sufficiently abundant and accurate to determine whether an enhanced liability to cancer is transmitted from parents to offspring. All the mice involved in the experiments are descended ultimately from animals known to have suffered from cancer. All the animals which did not present a tumor during life were carefully examined for tumors after death. The mice in which tumors were discovered during life were observed until death. They have been examined microscopically in every case. The results presented must be regarded as provisional. The figures refer to females only. There was a rapidly increasing proportion of deaths from cancer beginning after 6 months, attaining a maximum in the 3-monthly period ending at 18 months. In the succeeding periods, the frequency diminished, until in mice over 24 months old the frequency was barely twice that found in mice under 9 months old. Female mice in whose ancestry cancer of the mamma had occurred not farther back than the grandmothers were distinctly more liable to develop the disease spontaneously in this organ than those in whose ancestry cancer is more remote. The increased liability is probably of the nature of a predisposition of 1 particular tissue or organ system to undergo cancerous transformation under the wear and tear of life. The differences between the 2 groups were apparent at all ages, and the age of maximum incidence did not appear to have been lowered in the predisposed group. The magnitude of the difference was such that it could not be accounted for by the chances of random sampling.