Stromal tumor of the gallbladder with phenotype of interstitial cells of Cajal - A previously unrecognized neoplasm

We report a small, well-demarcated stromal tumor of the gallbladder in a 69 -year-old woman. The tumor and associated cholelithiasis led to chronic cho lecystitis symptoms. The wall of the gallbladder contained a 2.4-cm hypocel lular nodule composed of bland spindle-shaped cells that were immunoreactiv e for vimentin. CD34, and CD117. With the latter antibody, which stains int erstitial cells of Cajal (ICC), the neoplastic cells appear fusiform with e longated bipolar projections or dendritic-like cytoplasmic projections. The gallbladder wall adjacent to the tumor contained numerous CD117-positive c ells in close contact with the normal smooth muscle cells, whereas two of 1 0 gallbladders with minimal chronic cholecystitis showed only a few CD117-p ositive cells. These findings provide evidence that this stromal tumor of t he gallbladder shows ICC differentiation similar to some stromal tumors of the gut. The presence of numerous ICC in the uninvolved gallbladder wall su ggests that this tumor might have evolved through hyperplasia of ICC.