[Gastrointestinal stromal tumors. A case of small intestine stromal tumor (SIST) with an uncertain biological aspect].

Tumors of the small intestine are relatively rare. The diagnosis is difficult to establish because the symptoms are vague and non-specific. Although the small intestine constitutes 75% of the length and over 90% of the mucosal surface area of the gastrointestinal tract, only 1 to 2% of gastrointestinal malignancies occur in this segment. Metastases are usually present at the time of diagnosis. The outcome of these patients can be improved if the possibility of a malignant small bowel tumor is considered in all cases of unexplained abdominal pain or gastrointestinal bleeding, especially in younger age. Malignant tumors occur with increasing frequency in distal small bowel with a preponderance of malignant lesions in the ileum compared with the jejunum and the duodenum. Adenocarcinoma is the most common tumor of the primary malignant small bowel tumors, followed by carcinoid, lymphoma and leiomyosarcoma. Mesenchymal tumors of the gastrointestinal tract, traditionally regarded as smooth muscle tumors, have demonstrated different cellular differentiations based on immunohistochemical and ultrastructural features. Therefore the terms leiomyoma and leiomyosarcoma have been replaced by a more encompassing term, gastrointestinal stromal tumor (GIST). The majority of GISTs occurs in the stomach; stromal tumors involving the small intestine (SISTs) are far less common but seem to have greater malignant potential. The clinical a case of a small intestinal stromal tumor (SIST), localised in the jejunum and characterised by an uncertain histological aspect, is presented and a review of the literature is made.