Immunohistochemical expression of STAM2 in gastrointestinal stromal tumors.

Background: Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the digestive tract, believed to originate from the interstitial cells of Cajal or their stem cell-like precursors. Recent studies incidentally found the expression in interstitial cells of Cajal of the signal-transducing adaptor molecule-2 (STAM2), which is an endosomal protein acting as a regulator of receptor signaling and trafficking. Here, we investigated the immunohistochemical expression of STAM2 in GIST.

Materials And Methods: To evaluate the level of STAM2 expression, the percentage of cells staining positively for STAM2 and their staining intensity were graded on a scale of 0-3 and then multiplied to give the staining index as: 0=none; 1-3=low; 4-6=moderate and 9=high.

Results: In 51 analyzed GIST samples, expression of STAM2 was observed in 45 cases (88.2%). Based on antibody screening, we observed a positive correlation between the expression of GIST marker stem cell growth factor receptor, also known as tyrosine-protein kinase KIT or CD117, and STAM2 expression (r=0.387, p<0.003). To identify possible STAM2 function in GIST, we performed correlation analysis between STAM2 expression and tumor size, primary tumor site, tumor type, mitotic count, Ki-67 proliferative index, risk stratification and development of recurrent/metastatic disease. Among these parameters, only correlation between the percentage of STAM2-positive cells and mitotic count was statistically significant (r=-0.362, p<0.01).

Conclusion: Further studies are required to unravel the role of STAM2 in the oncogenic cell phenotype of GIST.