Analysis of CD117-negative gastrointestinal stromal tumors

Figure 1 Light microscopic examination of case #23 (A) shows interlacing spindle tumor cells (hematoxylin & eosin stain). The tumor cells were negative for CD117 by immunohistochemistry (B), while the adjacent mast cells were immunoreative to CD117 (C). This tumor was strongly positive for S-100 (D). (magnification ×400).

Figure 2 Proposed algorithm for the diagnostic approach to the primary mesenchymal tumor of the gastrointestinal tract. GIST (I) represents the prototypical GISTs, which were diagnosed based on positive CD117 by immunohistochemistry. If tumors were negative for both CD117 and S-100 but positive for α-smooth muscle actin or desmin, they were true smooth muscle tumors. The rest of the tumors should be examined for PDGFRA and KIT genes. Those harboring mutated PDGFRA, labeled GIST (III), belonged to the recently described entity[11], whereas those containing mutated KIT, labeled GIST (II), were described in this study. The remaining tumors were not GISTs.