Objective  This study aims to analyze the properties of gastrointestinal stromal tumor (GIST) with diameter of less than 2 cm and to discuss the probable mechanisms of GIST occurrence and development.

  Methods  Fifteen small-GIST and 56 overt-GIST samples were collected in the Department of Pathology, The First Affiliated Hospital of Fujian Medical University, from June 2008 to December 2010. PCR amplification, direct sequencing, and immunohistochemistry were employed after DNA extraction from paraffin sections to observe the clinicopathological characteristic of the GISTs during the pre-clinical period and to compare C-kit gene mutation among different clinical periods.

  Results  The small-GIST patients had an average age of 62.2 years old. Thirteen patients were accompanied by malignant epithelial tumor with an average diameter of 0.88 cm in their gastric tract or adjacent organs. Microscopically, most tumors are located in the seromuscular layers of the stomach without clear boundary, and their morphologies are spindled in most cases. Cellularity degree was low except for two cases with moderate intensity. Cellular atypia was not observed in any of the lesions. The nuclei tended to be more slender and somewhat wave accompanied central hyaline degeneration. In addition, the tumor hyperplastic interstitial cell of cajal was similar to the main tumor in morphology and CD117 and CD34 strong positive expression was observed immunohistochemically. C-kit gene mutation was detected in nine cases. The mutations involved exon11 in six cases, exon9 in one case, and exon13 in two cases. The overall mutation frequency of the small-GISTs was less than that of the overt-GISTs, but no significant difference was found.

  Conclusion  More evidence supported inert self-limited hyperplasia as a property of the GIST with diameter of less than 2 cm. C-kit gene mutation may be the early event in GIST genesis.