An increase in paper regarding eludidation of carcinogenic mechanism implies an importance of this problem. Especially, clarification of an interrelationship between carcinogenesis and change in hormonal evironments is of great interest, because hormone is a substance physiologically present in the body and it is possible to influence the states of the cancer cells. In this paper, the effect of hormones on prostate cancer was investigated by altering endocrine environments of the rats with this

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... tumor. The rate of occurrence of prostate cancer and the ultrastructure of the tumor were examined. The following results were obtained. 1. The rate of occurrence of prostate tumor; The rates were 8.69 % in a group of the rats which were subcutaneouslly inoculated 20-MC wrapped with prostate tissue, 10 % in a group of the rats which were subcutaneously inoculated 4 -NQO wrapped with prostate tissue, 20 % in a group of the rats that 20 -MC was intraprostatically applied, and 12.5 % in a group of the rats that intraglandular injection of 20-MC was combined with castration. The rates were, on the other hand, 2.78 % in a group of the rats with castration and 8.89 % in a group of the rats without castration. The results are suggestive of the presence of the effects altering endocrinological medium on tumor formation.