Abstract
1. Examination was made of 18 cases with ulcer-carcinoma in early stages by the serial section method.
2. Ulcer-carcinoma seems to originate from regenerative epithelium of atypical proliferation.
3. In 11 of the 18 cases with early ulcer-carcinoma, multicentric development of cancer foci has been demonstrated at the ulcer margin or in the mucous membrane apart from the ulcer margin. In the re-maining 6 cases, except 1 case in which a small cancer focus was found in a very small portion of the ulcer margin, cancer foci extended to surround the ulcer margin completely or almost completely, being thus suggestive of the fusion of multicentrically developed cancer foci.
