IMMUNOHISTOCHEMICAL EXPRESSION IN GASTROINTESTINAL STROMAL TUMORS (GIST) (A Clinicopathological study)

Gastrointestinal stromal tumor (GISTs) is the preferred term for mesenchymal tumors specific to the astrointestinal tract. GISTs include most tumors designated previously as cellular leiomyoma, leiomyoblastoma, and leiomyosarcoma. GISTs are composed of spindle or epitheliod cells 10%-30% are malignant showing intra abdominal spread or liver metastasis. They immonohistochemically positive for c-kit (CD117), CD34, and some times actin, desmin, NSE, and S-100 protein. Recent work has indicated that the Interstitial cells of Cajal (ICC), a complex net work postulated to act as a pacemaker cells of the gastrointestinal tract, which exhibit both myoid and neural features, could be candidate for the tumor histogenesis. This would provide a plausible and attractive explanation for the variable differentiation pathways identified in GIST category to date. Aim of the study: - To highlights the attention about GISTs and their histomorphological and immunohistochemical features and to evaluate their response to the molecular therapy (Imatinib Mesylate). Materials and methods: - Thirty four cases diagnosed as GISTs and other mesenchymal tumors by H&E stain during a six years period at different centers were selected for this study; all paraffin embedded sections were stained with H&E stain and also for immunohistochemical markers C-kit ,CD34, Desmin, S-100 protein. Results: - The mean age for patient involved in this study is 50.14 years with females to males’ ratio 1.26:1. The stomach affected most frequently (50%), followed by colon (17.6%), small intestine (14.7%), while the mesentery was affected by (5.9 %) and the rectum by (5.6 %) of cases and the retroperitoneum by (5.6%) from the all collected cases. About 52% of the tumors showed spindle cell proliferation, while mixed cell type composed 24% while18% were with epitheliod appearance and 6% were neuroid cell type. The immunohistochemical study showed 85% of the tumors positive for C-kit, 61.8% for CD34, 44% for S-100 protein and 9% were positive for Desmin. Conclusions: - The diagnosis of GISTs mostly relies on histopathological features However the immunohistochemical confirmation is necessary, and the most important immunohistochemical feature is the positivity of the tumor cells for CD117 and CD34. It, other markers as Desmin and S-100 protein are helpful to demonstrate & confirm the diagnosis of GISTs.
In our study ,the stomach is the most commonly affected part of the GIT followed by the colon, small intestine ,large intestine and extra Gastrointestinal sites like Retroperitoneum , Mesentery and Omentum
GISTs showed pluripotential differentiation rate as reflected by the co expression of different tumor markers included in this study 85% for C-kit,61% for CD34 ,44% for S100 and 9% for Desmin. C-kit expression has emerged as an important defining feature for these tumors identification, although it might be also expressed by other tumors affecting the GIT.