Cystic gastrointestinal stromal tumors of the pancreas simulating cystoadenocarcinoma. Report of three cases and short review of the literature.

Gastrointestinal stromal tumors (GISTs) represent a distinct subset of mesenchymal tumours of the gastrointestinal tract. They are more common in the stomach and small intestine, and are characterized by the proliferation of spindle or epithelioid cells and by the expression of CD117. Extra-gastrointestinal stromal tumors are rare and only 13 cases of pancreatic GISTs have been reported in the literature, only 1 of which presented as a cystic lesion. Mutational analysis of KIT and Platelet derived growth factor receptor-α genes was performed only in two out of the 13 cases. We report 3 cases of cystic GISTs of the pancreas, radiologically mimicking a cystoadenocarcinoma. Routine histopathology and molecular characterization of the tumours have been performed. In two of them, molecular analysis showed unusual genetic alterations (the internal repeat of codon 502 and 503 in exon 9 of the KIT gene and the KIT exon 9 single nucleotide substitution c.1427G⟩T). Pancreatic GIST should be included in the differential diagnosis of both cystic and solid masses of the pancreas. The diagnosis should be accomplished by a combination of radiology, histology, immunohistochemistry and molecular biology. The evaluation of CD117 expression and the sequence analysis of KIT and Platelet derived growth factor receptor-α gene is mandatory for therapy.