A morphologic curiosity is presented in a polypoid gastric tumor combined with adenocarcinoma and carcinoid tumor. It is likely that those two represent a composite tumor; however, the authors think it is more likely that they are two concurrent, independent collided tumors.

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Gastric carcinomas hidden beneath flat and intact mucosal surface epithelium are rarely discovered. Such a tumor in the early stage is at best diagnosed as an incidental finding, so that the diagnosis is probably always a surprise to the clinician. Six such cases of early gastric carcinoma were presented. Four were intramucosal lesions and the remaining two were invasive with submucosal extension. All the tumors are composed purely of signet-ring cells (diffuse-type by Lauren's classification). Histologic examination of the six cases revealed that certain features, which are not characteristically observed in ordinary signet-ring cell carcinomas, were commonly recognized. These included compact nests of uniform signet-ring cells sharing a common cytoplasmic wall, lack of desmoplastic stromal response, and intracytoplasmic mucin predominantly composed of neutral mucopolysaccharide. These six tumors are considered to be an incipient stage of signet-ring cell carcinoma. The findings also suggest a close histogenetic relationship between these tumors and the mucous neck cells in the basal region of gastric glands. The grossly unremarkable mucosal surface and histologically innocuous appearance associated with this form of tumor are emphasized for diagnosis.

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