微小未分化型胃癌の発生母地と発育進展様式―分化型癌と対比して

Histogenetic Backgrounds and Growth Pattern of Undifferentiated Type Microcarcinoma of the Stomach: In Comparison with Differentiated Type Microcarcinoma

要旨　未分化型胃癌の発生母地（周囲粘膜）には，分化型に比べて明らかに腸上皮化生の発生頻度が低かったが，約40％の症例において少なくともどこかに腸上皮化生がみられた．未分化型癌を印環細胞癌と低分化腺癌に分けて検討すると，胃底腺領域に発生した印環細胞癌の発生母地は全例，化生や偽幽門腺のない胃底腺粘膜であったが，低分化腺癌では，大多数が化生や偽幽門腺を含む粘膜であった．未分化型の発生母地は印環細胞癌と低分化腺癌で異なると考えられた．胃癌の発生初期における発育進展様式を肉眼的立場からみると，未分化型は1mm前後は平坦型であり，2～3mmを超えて陥凹型となり，大きさの増大と共にこの傾向が顕著になった．分化型は，最初から陥凹型を示すものが多く，5mmまでは陥凹型か平坦型で，隆起型は5mmを超えてから増加した．組織学的立場からの考察も行った．

　To elucidate histogenetic backgrounds of undifferentiated type carcinoma (UCA) of the stomach, we investigated the incidence of intestinal metaplasia or pseudopyloric gland in the mucosae adjacent to (0-0.5 mm) and a few millimeter (2-3 mm) away from the microcarcinoma (carcinoma of 5 mm or less in the largest diameter, n=12) located in the fundic gland area. No significant difference in incidence of these changes was observed between the two separate mucosal sites around the carcinoma. When these UCA were classified into either signet ring cell type or poorly differentiated type, the lesion was surrounded by the fundic gland mucosae without intestinal metaplasia or pseudopyloric gland in all cases (n=7) of the former type, while it was accompanied by at least one of these mucosal changes in the cases of latter type. Hence, the histogenetic background of UCA should be considered separately for each subtype.

　Furthermore, observing gross appearance of microcarcinoma made it possible to investigate growth pattern of UCA in its very early phase in comparison with that of differentiated type carcinoma (DCA). Most (80.0%) of the UCA, particularly of signet ring cell type, were of flat type (Ⅱb) when the lesions were less than 3 mm. With the lesions 3 mm or more, the incidence of flat type fell to 28.6% and, instead, that of depressed type (Ⅱc) rose to as high as 71.4%. On the contrary, most of the DCA remained Ⅱc or Ⅱb throughout the stage of microcarcinoma. The elevated type was infrequent even among the cases with the lesion of 5 mm in size. Therefore, UCA in its very early stage seemed to grow more frequently in flat fashion than in depressed fashion compared to DCA.

　Discussion was also made regarding the relationship between histological change and growth pattern.