Diagnostic Significance Of DOG-1and PKC-θ Expression And C-kit/PDGFRA Mutations In Gastrointestinal Stromal Tumors

Background Gastrointestinal stromal tumors (GISTs) are a subtype oftumors originating from gastrointestinal mesenchymal tissues.The diagnosis ofGISTs is mainly dependent on morphological features and immunologicalstaining (i.e. KIT/CD117) in combination with detection of biomarkers ofsmooth muscle cells and nerve-derived differentiation markers (i.e. to excludegastrointestinal muscle or nerve derived tumors). Immunohistochemistry (IHC)for CD117and CD34is the most valuable method for diagnosing a GIST.However, clinical data have shown that in about4%to10%of casesimmuno-negative for CD117, the histological analysis suggests the existenceof gastrointestinal stromal tumors. It is known that other tumors can expressCD117, including melanoma, endometrial stromal tumors, adenoid cysticcarcinoma, and solitary fibrous tumor. Some of these tumors are difficult todistinguish with GISTs. Recent studies using gene expression profiling haveidentified two genes highly expressed in GISTs, DOG-1(Discovered OnGIST-1) and protein kinase C-θ (PKC-θ). DOG-1is a calcium-dependentreceptor-activated chloride ion channel protein[41]. Studies have shown thatDOG-1has a better sensitivity and specificity in the diagnosis of GISTs thanCD117[3]. About30%of the CD117negative cases are DOG-1positive. PKC-θis also overexpressed in GISTs[4]. In particular, PKC-θ has an importantdiagnostic value in CD117-negative GISTs. Only a few studies have evaluatedthe sensitivity of DOG-1and PKC-θ for the diagnosis of GISTs.Objective To investigate DOG-1and PKC-θ expression in GISTs to determine the sensitivity, specificity and diagnostic value of these twoantigens.Methods Immnunohistochemistry (IHC) was used to detect CD117,DOG-1, PKC-θ, CD34, Ki-67, α-SMA, S100and Desmin expression in147GISTs and51non-GISTs. c-Kit gene (exons9,11,13and17) and PDGFRAgene (exons12and18) mutations were also detected.Results139out of147(94.5%) GISTs were immuno-positive for CD117,141out of147(96%) were for DOG-1while133out of147(90.5%) were forPKC-θ. DOG-1had a specificity of100%, while CD117and PKC-θ had aspecificity of90%and80%, respectively. There was no significant differencebetween DOG-1and PKC-θ expressions when compared to CD117expression. CD117was detected in9.8%non-GISTs, including4cases ofadenoid cystic carcinoma and1case of melanoma. PKC-θ was expressed in4cases of leimyoma,1case of melanoma and5cases of neurilemmoma. Allcases were DOG-1negative. In30out of42(71.5%) GISTs a c-Kit genemutation was found; and in3out of42cases (7%), PDGFRA was mutated.Wild type c-Kit/PDGFRA genes accounted for21.5%(9/42). Most c-Kit genemutations were found to be located at exon11, mainly as in-frame deletions.Mutations in exon9were all missense mutations. Most PDGFRA genemutations were found in exon18, codon842. c-Kit gene mutations in exons13and17, and the PDGFRA gene mutation in exon12were not detected.Conclusions1. DOG-1expression has slightly higher thanCD117.compared to CD117, DOG-1is a biomarker with higher sensitivity andspecificity. In combination with CD117, DOG-1can be used to improve thediagnosis of GIST.2. PKC-θ can be applied as a useful biomarker, especiallyin CD117and/or DOG-1cases.3.The majority of GIST occur c-Kit genemutations, some PDGFRA mutations in GIST cases occur the case of c-kit gene mutations existence;4.c-Kit gene mutation mainly occured in exon11,followed by exon9, PDGFRA gene mutation mainly occurred in exon18;5.CD117-negative cases and PKC-θ-negative cases both had c-Kit exon11and （or）PDGFRA mutation, This indicates detection of c-Kit and PDGFRAmutations are valuable for GIST diagnosis and help determining the treatmentoptions of patients with gastrointestinal stromal tumors.