前立腺腫瘍の実験的研究 I: 20-Methylcholanthreneによる前立腺腫瘍の発生

Abstract

Prostatic cancer is characterized by hormone de p endence, frequent presence of latent cancer and increased occurrence with advance of age, all of which are subjects of interest. Howev'r spontaneous development is not known in the Rodentia and experimental devel opment is widely studies due possibly to the fact that the clinical picture of the prostatic cancer differs greatly from the experimental cancer. This has brought us very few knowledges about the mechanism of carcinogenesis. On these points of view, experimental studies were performed by administrating 20-methylcholanthrene to Wistar strain rats which have less occurence of spontaneous carcinoma. The purpose of the study is to clarify the way of progress of carcinogenesis in animals given carbohydrate compounds and to observe the process of undergoing changes of cells toward cancer. Into the anterior lobe of the prostate, 0.1 m l of 3 % solution of 20-methylcholanthrene in Tween 80 was injected and development of tumor was observed for 6 month period. The initial development of tumor was recognized 88 days after injection. The occurrence rate of tumor in the first group of animals which was observed for 100 days, in the second group observed for 180 days and in the third group followed up than 181 days were 25 %, 60 % (3 out of 5 animals) and 58.9 % (10 out of 17 animals) respectively, so that in total the tumor was demonstrated in 53.9 % (14 out of 26 animals). Histological examination revealed squamous cell cancer in 10 out of 14 tumors, papilloma in 2, sarcoma in 1 and mixed adenoma in 1. As the p r o cess of formation of the tumor, one can suspect that squamous metaplasia of the glandular epithelia is taken place accompanied by chronic inflammation with granulation or abscess due to 20-MCT administration and this is followed by a gradual but irreversible transformation of keratinized squamous cell carcinoma around 180 days after administration therefore the squamous cell metaplasia and carcinomatous change is not considered to be a different disposition but is supposed to be a contineous process of morphological changes. Accordingly, a frequent development of prostatic cancer from the senilly atrophic glandular tissue observed in clinically is seemed to be due to the fact that the latant cancer-rearing factor is brought into existence by a mutation of the cells, of which biological functions are detereorated. This speculation can extend to the results of our study that formation of the initiating factor is progressed under the circumstance of chronic inflammatory stimuli of 20-MCT which is followed by additional participation of the promoting factor. Althogh DNA is participated as the source of energy for unlimited proliferation of cancer cells, an additional high leveled factor is suspected to take a part in the development of cancer as the promoting factor.