Predictive value of KIT immunohistochemical staining for KIT mutations in patients with gastrointestinal stromal tumors (GIST): A systematic review.

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30 Background: Immunohistochemical staining for KIT (CD117) is used as part of diagnostic tool for GIST. Approximately 95% of GIST are known to be positive for CD117. Studies have shown that not all CD117-positive GIST carry KIT mutations nor does CD117 negativity rule out KIT or PDGFRA mutations. We performed a systematic review to investigate the positive and negative predictive values of KIT immunostaining for KIT mutations in GIST. Methods: A Medline search of the MeSH terms “KIT mutation” and “GIST” and “prevalence” yielded 54 articles from year 1999 to 2011. English language studies on GIST with data available for KIT immunostaining as well as KIT gene mutations were included. Studies lacking data on either CD117 positivity or KIT mutations were excluded. Immunostaining was done using Dako polyclonal rabbit antibody or PKCh monoclonal mouse antibody in eligible studies. Denaturing high-pressure liquid chromatography (DHPLC) was used to screen mutations in majority of eligible studies, and ABI Prism Genetic Analyzer to sequence DNA. Results: 6 studies including 708 CD117-positive GIST patients were eligible for analysis of positive predictive value of KIT immunostaining for KIT mutations and 5 studies including 47 CD117-negative GIST patients for negative predictive value. Many studies were excluded due to insufficient data on CD117 positivity or KIT mutational analysis. 72.8% of CD117-positive GIST tumors carried KIT mutations (exon 11 62.2%, exon 9 10.2%, exon 13 1.8% and exon 17 1%), and 4.1% harbored PDGFRA mutations. In contrast, 74.5% of CD117-negative GIST tumors did not have KIT mutations. 25.5% of CD117-negative GIST harbored KIT exon 11 mutations (no mutations in exon 9, 13 or 17 were observed). In addition, 30% of CD117-negative GIST were found to have PDGFRA mutations. Conclusions: PDGFRA mutations were found to be 7 times more common in CD117-negative than in CD117-positive GIST (30% vs. 4.1%). Over half (55.5%) of CD117-negative GIST carried KIT exon 11 or PDGFRA mutations. We recommend mutational analysis in all tumors clinically suspected of GIST and that are CD117-negative for two reasons: 1. in order to make a diagnosis, and 2. to help tailor therapy.