Relationship between mucin expression of gastric intramucosal signet ring cell carcinoma and its background mucosa.

The intramucosal lesion of gastric signet ring cell carcinoma (SIG) is known to form a layered structure (LS) that simulates mucin expression in ordinary gastric mucosa. In this study, we suspected the influence of background mucosa on the formation of LS and performed histopathological analysis. We examined 35 cases of intramucosal SIG with a maximum diameter of 30 mm or less. The LS patterns were classified into those with a layer of MUC6-positive cells (complete pattern, CP) and those lacking this layer (incomplete pattern, ICP). The relationship between LS patterns and the characteristics of the background mucosa, the expression of MUC2 (intestinal-type mucin antigen), MUC5AC (foveolar-type mucin antigen), and Ki-67 (the marker of cell proliferation activity) was examined by histochemistry and immunohistochemistry. Intestinal metaplasia in the background mucosa and MUC2 expression were frequently observed in cases with ICP. Ki-67-positive cells were much more and they were distributed more widely in the lesion of cases with ICP alone than in the other cases. Mucin expression and LS formation of gastric SIG are strongly influenced by its background mucosa. The cases completely lacking MUC6 expression may have higher malignant potential.