A New Theory on the Cancer-inducing Mechanism

RECENT research in genetics and pathology has shown an amazing consistency between the agents causing mutations and those causing-or contributing to the development of-cancer. One of the more prominent theories, which since the 1920's has been advocated by Bauer (1949), Strong (1949) and others, claims that the original cancerous cell is nothing but an ordinary cell affected by genetic mutation of some kind. One of the main objections to this theory has been that it does not explain the age variation of the cancer frequency. In reply, Bauer (1949) contends that the mutated cells apparently remain latent during a long period until the new qualities become evident and the phenomenon can be diagnosed as cancer. Bauer has found this period of latency to average 9 years for X-ray cancer, 12 years for paraffin cancer, 18 years for aniline cancer and 40 years for seaman's cancer (caused by solar radiation). The early occurrence of sarcoma and of leukaemia, however, does not conform to the idea of a latent period. Moreover, it appears somewhat unreasonable to suppose that the length of the latency period would depend upon whether the mutation is caused by sun-rays or by X-rays. Writh most forms of carcinoma, furthermore, the frequency at different ages is such that wre are compelled to consider average latency periods of 70 years or more, in order to explain the actual age frequency curve of cancer mortality in man. These facts still make it difficult for many of the most competent authorities in the field to accept the mutation theory without reservations. Dahlberg (1943) has advanced a completely different explanation concerning the relationship between age and cancer. He expressed the opinion that malignant tumours develop increasingly easily with rising age. This implies that, for the development of tumourous cells, it is necessary for a certain number of cellular divisions to have taken place, between each of which there has been a certain period of time. All experience concerning the cancerous influence of chronic irritations promoting cellular divisions seems strongly to support this theory. The question then arises of the nature of the process taking place in the cells during the intervals between their various divisions. According to the theory advanced in 1934 by Timof6eff-Ressofsky, Delbruck and Zimmer (1935) and discussed by Schroedinger (1944), mutations constitute such a process, which goes on incessantly in every large group of cells. Mutations are caused, according to …