There are some different opinions on the natural history of gastric adenoma followed 3 years or more ; one is no remarkable change, and the other is that the tumor increases in size at 31% and shows malignant transformation at 15%. In these reports, histological criteria seem to be different. Therefore, I myself examined the initial biopsy-sections of 51 lesions (48 patients) originally diagnosed as gastric adenoma which was or has been followed up 3 years and more. Results ; The initial biopsy-section consisted of 9 differentiated-type adenocarcinomas with low-grade atypia, and 42 tubular adenomas. Thirty-five tumors including 2 carcinomas did not change in size and shape, but 16 tumors including 7 carcinomas in-creased in size during the follow-up period. Four of the 7 carcinomas changed into a high-grade carcinoma at the surgically resected time and showed a high growth-rate (2-6 times the initial size) during 3-6 years, and the remaining 3 carcinomas was still low-grade in atypia but increased 1.5 times the initial size during 3-5 years. Five of the 9 adenomas in the size-increased group changed into a low-grade (predominat) carcinoma with (2 tumors) or without adenoma. They grew up 1.5-2.0 times the initial size during 3-9 years. Four size-increased adenomas grew up to 1.3-1.7 times the initial size during 4-9 years. The low-grade (predominat) carcinomas and adenomas revealed a lower growth-rate than the high-grade (predominat) carcinomas. Conclusion ; It is concluded that the gastric tumor with well-developed tubules should histologically be classified into adenoma, low-grade carcinoma and high-grade carcinoma and that each tumor shows a different growth-rate and biological behavior, i. e., gastric adenoma is generally very slow in growth, but its growth greatly depends on the development of carcinoma as well as on histological grade of its malignancy.

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