OBJECTIVETo study the immunophenotype and c-kit or platelet derived growth factor receptor alpha (PDGFRA) gene mutations in CD117-negative gastrointestinal stromal tumors (GISTs).

METHODSTen cases of GISTs with typical histologic features but no CD117 expression were retrieved from the archival of Department of Pathology, Peking Union Medical College Hospital, China. The cases were further evaluated for the presence of c-kit exons 9, 11, 13 and 17 mutations and PDGFRA exons 12 and 18 mutations. DNA was extracted from the paraffin-embedded tumor tissue. The PCR products were sequenced directly for the mutations. An immunohistochemical study for CD117, CD34, smooth muscle actin, desmin, S-100 protein, WT-1 and DOG-1 was also performed.

RESULTSEight of the 10 cases had the mutation tests completed. C-kit mutation in exon 9 was detected in only one case. Amongst the 10 cases studied, CD34 was expressed in 9 cases. Smooth muscle actin was focally positive in 2 cases. None of them expressed desmin or S-100 protein. DOG-1 and WT-1 were diffusely positive in 5 and 4 cases, respectively. In addition, DOG1 was diffusely but weakly positive in 1 case and focally expressed in 2 cases. Three cases were focally positive for WT-1.

CONCLUSIONPathologic diagnosis of CD117-negative GISTs can be facilitated with the application of a panel of immunohistochemical markers, including DOG-1 and WT-1.