[Clinicopathological features of small intestinal tumors]

Small intestinal neoplasms are rare, accounting for only 1-2% of all gastrointestinal neoplasms. Variable neoplasms are recognized in the small intestine. Comparatively frequent malignant lesions are carcinoma, carcinoid tumor, malignant lymphoma, and GIST (gastrointestinal stromal tumor). The prognosis of small intestinal cancer is poor, because preoperative diagnosis is difficult and it is usually discovered at the advanced stage. In addition, it is thought that there are few small intestinal cancers of an adenoma origin, but dysplasia is considered to be associated with that complicated by Crohn's disease. The incidence of carcinoid tumor is lower in Japan than in Western countries. Although it is often discovered at the advanced stage, its prognosis is relatively good in spite of the high incidence of metastasis because of its low-grade malignancy. Among malignant lymphomas of the small intestine, the incidence of MALT lymphoma is lower, and those of T cell and follicular ones are higher than in the stomach. Lymphomas with minimal cellular atypia are often encountered, and in such cases biopsy diagnosis is difficult. The prognosis of small intestinal lymphoma is better than for small intestinal cancer. It must be recalled that multiple GIST occurs in specific disorders such as von Recklinghausen's disease and familial disease among small intestinal GIST, although very rarely. The prognosis of malignant small intestinal disease will improve through early diagnosis with the recent progress in the procedures for detecting small intestinal disease.