An Approach to Diagnosing Gastrointestinal Stromal Tumors Using Immunohistochemistry of c-kit and PDGFRA with Molecular Analysis

Background : Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors in the gastrointestinal tract. Recently, many methods for the diagnosis of GIST have been developed including molecular diagnosis. Methods : We selected 90 cases of GIST that had presented at Kyungpook National University Hospital between 1998 and 2007. Tissue microarrays were made using core areas of tumor tissues. Immunohistochemical staining for c-kit, protein kinase C-theta, and platelet-derived growth factor receptor alpha (PDGFRA) was done. Direct sequencing of hot spot exonal areas for c-kit and PDGFRA were done using extracted DNAs of all 90 paraffin block tissues. Results : Among the 90 cases, 83.3% (75/90) were c-kit positive, 16.6% (15/90) were c-kit negative, 93.3% (84/90) were PDGFRA positive, and 6.6% (6/90) cases were PDGFRA negative. Fifteen cases of c-kit negative GIST included 1 case of PDGFRA negative and 5 cases of PDGFRA negative GIST were c-kit positive. The one case in which both c-kit and PDGFRA were negative, showed a c-kit mutation in exon 11. Conclusions : Combined immunohistochemical staining of c-kit, discovered on GIST 1 (DOG1) and PDGFRA is helpful for the diagnosis of GIST. When all staining tests are negative for immunoreactivity, c-kit mutation analysis for exon 11, 9 should be done. Genotyping of kit and PDGFRA do not need to be examined initially, if it is only for the diagnosis of GIST.