Mast cells or not? - CD117 positive cells in esophageal leiomyoma

The presence of CD117 positive cells in esophageal leiomyoma may lead to a misdiagnosis of GIST. We reviewed 46 esophageal tumors which were smooth muscle tumors or GIST. Based on morphology, immunohistochemistry and mutation analysis, there were 44 (95.6%) leiomyomas, 1 (2.2%) leiomyosarcoma, and 1 (2.2%) GIST. Variable numbers of CD117 positive cells were seen in all leiomyomas. Tryptase immunostaining identified mast cells in 93.2% (41/44) of leiomyomas, and the number of mast cells per tumor decreased significantly from tumors of the upper esophagus to the esophageal-gastric junction (p<0.01). Immunofluorescence study further confirmed the presence of two types of CD117 positive spindle cells which included spindle-shaped mast cells and DOG-1-positive interstitial cells of Cajal. This is the first study to systemically review mast cells in esophageal leiomyomas and tumors which may be included in the differential diagnosis. We demonstrate that both spindled mast cells and hyperplastic interstitial cells of Cajal are present within esophageal leiomyomas. The immunoreactivity of these cells with CD117 may suggest a diagnosis of GIST, but the presence of mast cells itself supports a diagnosis of esophageal leiomyoma.