α-fetoprotein producing gastric cancer (AFP-GC) rarely occurs, but it is classified as a special subtype of gastric cancer (GC). This tumor, as represented by the production of AFP, exhibits not only specific function but also different histology compared with ordinary-GC (O-GC). Clinically, it is likely to metastasize to the liver and, as a consequence, poor prognosis is recognized as one of the features. Recently, AT motif binding factor-1 (ATBF1) was identified as a modulator of AFP production by hepatocellular carcinoma, and the decreased expression of the protein was also reported in AFP-GC. However, little is known about the biological significance of the decreased expression. In this study, to clarify the biological characteristics of AFP-GC, antibody was raised against ATBF1 and immunohistochemistry was carried out. The antibody specifically recognized ATBF1, and the degree of expression could be characterized by immunohistochemistry. ATBF1 was expressed in O-GC and the area of tubular adenocarcinoma components of AFP-GC. On the other hand, the expression pattern varied in the hepatoid carcinoma components of AFP-GC, and AFP was expressed in the area without ATBF1 expression. Taken together, these results corroborated the previous reports that ATBF1 regulated AFP expression and inhibited transcription. Furthermore, in terms of differentiation induction, ATBF1 expression was decreased in the areas with little glandular formation. This may suggest that aberrant expression of ATBF1 induces the expression of various factors that are otherwise suppressed, and that this somehow determines the biological features of AFP-GC.

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