[An immunohistochemical and ultrastructural survey on smooth muscle tumors of the alimentary tract].

33 cases of smooth muscle tumors of the alimentary tract were analysed. Among them, 18 cases showed positive reaction to desmin, including one out of two cases of esophageal neoplasms, 6 out of 11 cases of gastric neoplasms, 5 from 12 cases of small intestinal neoplasms, 6 from 8 cases of large intestinal neoplasms, 14 out of 21 cases of benign tumors as well as sarcomas in grade I, and 4 from 12 cases of sarcomas in grade II and III (only mild positive result obtained in grade II and III-sarcomas). S-100 protein staining was performed in 27 cases and positive reaction was obtained only in five. Among them, 2 cases showed prominent positive reaction. 20 cases were studied by electron microscopy, and cytoplasmic myofilaments as well as dense bodies were demonstrated in 7 cases. All of them were the benign neoplasm or sarcoma in grade I. The conclusion is that most stromal tumors of the digestive system are originating from the smooth muscle, except very few cases are neurogenic in origin.