Immunohistochemical expression of STAM2 in gastrointestinal stromal tumors

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.

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.

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).

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