Is Malignancy Due to a Process Analogous to Somatic Mutation?

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Abstract
Malignant tumors develop in the walls of parasitic cysts of Cysticercus fasciolaris, the larval stage of Taenia taeniaeformis (crassicollis) the common tape worm of the cat. Tumors were produced experimentally by feeding rats Taenia eggs derived from cat feces. The analysis included chiefly data on 52,223 rats from pedigreed matings. Of these, 26,172 were infested with the parasite; 13,120 survived the infestation for at least 8 mos. (the minimum period of infestation observed in the case of a bearer of a Cysticercus sarcoma) and 3,285 had Cysticercus sarcoma. The rats were of several different strains and they showed marked strain and family differences in the proportion of individuals which developed both the disease and the complication. The duration of irritation (that is the period of residence of the parasite in the liver) was 8-27 mos. and the proportion of tumor-bearers increased directly from the 8th to the 20th mo. There was a significant negative correlation ([long dash] .527 [long dash] .008) between the number of cysts in the liver and the duration of infestation with the parasite, that is, the greater the number of cysts, the shorter the time before the appearance of a tumor. All the different strains considered separately showed the same general tendency to an increase in proportion of tumors and a decrease in the duration of infestation of the tumor bearers with an increase in the number of parasitic cysts. The observed strain and family differences were determined by 2 factors, relative longevity and susceptibility to Cysticercus disease. Since an increase in the number of cysts, i.e., an increase in the surface 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, it is apparent that chance is an important factor in the change of a normal to a cancer cell. This change may be analogous to somatic mutation.

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