The Respective Rôles of Heredity and Somatic Mutation in the Origin of Malignancy

Abstract

In their studies of induced Cysticercus sarcoma the authors found that an increase in the number of cysts, that is, an increase in the surface area exposed to the irritant, decreased directly the time interval necessary for the onset of the malignant process and increased directly the probability of its occurrence until it became inevitable. They therefore concluded (1) that chance was an important factor in the change of a normal cell to a cancer cell. They have shown further that in the case of Cysticercus sarcoma hereditary factors influenced the occurrence of malignancy only in so far as they determined the longevity of the individual and its susceptibility to Cysticercus disease. The Cysticercus cysts and the tumors showed (2) a fortuitous distribution to the several lobes of the liver, and the type of Cysticercus tumors observed represented the types of cells found in the cyst wall, each being represented by a number consistent with the expectation that the change of a normal to a cancer cell results from the chance action of an irritant. It would seem, therefore, that with the use of a carcinogenic agent which is more rapidly effective and can be distributed mechanically, differences resulting from the hereditary control of the duration and extent of irritation might be eliminated. The induced tumors would be expected to show a chance distribution to the injected loci in individuals of any genetic constitution or species, the type of tumor and the time from the injection of the irritant to the onset of the malignant change depending upon the character and the number of cells exposed.