Keratin-positive gastrointestinal stromal tumor of the stomach mimicking gastric carcinoma: diagnosis confirmed by c-kit mutation analysis.

In routine practice, gastrointestinal stromal tumor (GIST) can usually be identified with relative ease on the basis of a rather simple immunohistochemical panel besides its characteristic morphology. Still, serious differential diagnostic problems may arise because of the heterogeneity of these tumors in both morphologic appearance and clinical behavior. In our case, we present a metastatic, ulcerative, hemorrhagic GIST with epithelioid appearance, which displayed diffuse pan cytokeratin (AE1/AE3) positivity beside CD117 expression. As carcinomas may also be CD117-positive, definitive diagnosis was confirmed by the detection of a hexanucleotide deletion in the exon 11 of c-kit. This case demonstrates that although gastric carcinoma more commonly ulcerates or causes hemorrhage than GIST, keratin-positive GIST should also be considered from a differential diagnostic point of view. In these cases, c-kit mutation analysis may be necessary.