Analysis of CD117-negative gastrointestinal stromal tumors.

AIM: To identify the gastrointestinal stromal tumors (GISTs) that are negative for CD117 expression by immunohistochemistry and to characterize their malignant potential.

METHODS: A total of 108 primary mesenchymal tumors of the gastrointestinal tract were screened to select CD117-negative tumors, from which KIT (exons 9, 11, 13, and 17) and PDGFRA (exons 10, 12, 14, and 18) were sequenced to identify GISTs. Tumor recurrence and distant metastasis were used as the criteria of malignancy.

RESULTS: The result showed that approximately 25% (29/108) of the gastrointestinal mesenchymal tumors were negative for CD117 and approximately 6% (7/108) of the tumors were CD117-negative GISTs. All these CD117-negative tumors had a mutated KIT and a wild-type PDGFRA. All CD117-negative GISTs with mutations at codons 557/558 of KIT had mitotic counts >10/50 high power field, and 75% (3/4) of them showed multiple recurrence or distant metastasis.

CONCLUSION: CD117-negative KIT mutated GISTs account for approximately 6% of the gastrointestinal mesenchymal tumors. Tumor recurrence or distant metastasis correlates to both the KIT mutations at codons 557/558 and the mitotic counts, but not to the tumor size.