IMMUNOHISTOCHEMICAL STUDY ON 101 CASES OF GASTROINTESTINAL STROMAL TUMORS-AN ATTEMPT TO EVALUATE THE HISTOGENESIS

Gastrointestinal stromal tumors (GISTs) have generated considerablecontroversy about histogenesis, particularly whether the tumor cells are smooth muscle cells or Schwann cells. In order to characterize these tumors, the immunohistochemical staining patterns of vimentin, HHF-35 (muscle-actins), desmin and S-100 protein were studied in 101 cases of GIST (including 37 benign and 64 malignant). The results are also compared with normal host smooth muscle and 12 cases of extra-gastrointestinal smooth muscle tumors. Of these tumors, 94% were marked with vimentin (94.6% benign and 93.8% malignant), 65.3% were marked with HHF-35 (67.6% benign and 64% malignant), 23.8% were marked with desmin (37.8% benign and 15.6% malignant) and 22.8% were marked with S-100 protein (27% benign and 20. 9% malignant). There were 29 cases, neither marked with HHF-35 nor desmin, which showed also negative staining with neurofilament and GFAF. The reactivity of the tumor tissues to HHF-35 and desmin is much less than normal smooth muscle and tissues from extra-gastrointestinal smooth muscle tumors. These tumors are often diffuse and strongly stained with vimentin, a more primitive messenchymal marker. The finding indicates that most of the GISTs are of smooth muscle origin, but relatively undifferentia-ted. Esophageal GISTs tend to be most advanced in terms of smooth muscle differentiation. The morphology resemble uterine leiomyomas and expression of HHF-35 and desmin. On the other hand, gastric and intestinal GISTs are of varied differentiation in tumors. HHF-35 revealed positivity in some cases of GISTs in which desmin was not observed, especially in malignant tumors, suggesting that this antibody might detect less differentiated states of muscle cells better than anti-desmin antibody does.