Correlations Among Gene Mutation Status And Immunohistochemistry,Clinicopathological Features In Gastrointestinal Stromal Tumors

AimsGastrointestinal stromal tumors (GISTs).which originate from interstitial cells of Cajal(ICCs).is known as the most common gastrointestinal mesenchymal tumors.ICCs were demonstrated as the pacemaker cells of gastrointestinal tracts,but they also had characteristics of stem cells. The positive expression of CD117in immune phenotype and high frequencies of gene mutations in c-KIT or PDGFRA (platelet-derived growth factor alpha) gene are the most important biological characteristics of GISTs.But there are still5-10%GISTs are CD117-negative.For diagnosis of this group in GISTs patients, DOG1(Discovered on GISTs-1) has been a hotspot in recent years. Some researches has recommanded that its sensitivity and specificity may be higher than thses of CD117. With deeper studies in GISTs, molecular targeted therapy with tyrosine kinase receptor inhibitors (TKIs) has become the first-line treatment of metastatic GISTs.Linking TKIs with surgery, therapy for GISTs patients has entered a new era of individuality based on molecular typing, especially for those who harbor sensitive mutations’types to TKIs.5-10%GISTs lack c-KIT or PDGFRA gene mutations, called wild-type GISTs.GISTs’ biological characteristics are prone to metastasis and recurrence.Depending the theory that sensitivity to TKIs was different among gene mutant status.,we have to explicit patients’ mutation types.Then we can use datas as basis for making individualized treatment plan. The wild-type GISTs(wt-GISTs),of whose prognosis is often poor,have no indications for application of TKIs treatment.In recent years, some new mutations had been found in genetic analysis of GISTs, such as BRAF gene "V600E" mutation of exon15in wt-GISTs and PIK3CA gene mutations of exon20.These mutations were reported in other malignant tumors and there were some relations between them and the malignant behaviors of tumors. IGF1R (insulin-like growth factor receptor-1) expresses in wt-GISTs,In these patients, IGF1R’s coding gene had amplificated, but no mutations was described.Correlations among GISTs’ gene mutation status,clinicopathological features(including patient age, gender, primary tumor site, tumor size, tumor risk classification, etc.) and immunohistochemical expressions had no unified conclusions between domestic and foreign researches.This phenomenon may be related to ethnic differences. In our study, we use matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) to detect the common gene mutations that has been reported in77cases of GISTs.Then through statistical analysis to find relations among mutation types, clinicopathological features and immunohistochemisty.MethodsWe collect materials of77pathologically confirmed GISTs with completed clinical datas in Nanfang Hospital from2001-2010.We plus immunohistochemistry detection of DOG1and IGF1R to the existing datas. After extracting DNA from every cases’ paraffin tissues,we use MALDI-TOF-MS to detect gene mutations. Then we stratifies patients based on clinicopathological features and immunohistochemistry, then using χ2test to analyze correlations among gene mutation status,clinicopathological features and immunohistochemical expression (just focusing on CD117, DOG1and IGF1R). MALDI-TOF-MS is a new molecular biological technique that has been applied to detect and analyze macromolecular biologically active substances. Compared with the traditional direct sequencing, it has advantages of high accuracy, high precision and short testing cycles. Its limitations locus on the defects that this thechonology can just detect mutation which has been reported.ResultsThe77GISTs in our study showed a total gene mutation rate of64.94%(50/77) and22.08%(17/77) for c-KIT and PDGFRA gene, respectively.The genotypes for patients with c-KIT gene mutations showed as follows, exon11mutations was detected in27cases (54.00%,27/50;35.06%,27/77), exon9mutations was found in16cases (32.00%,16/50;20.78%,16/77),4cases harbored exon13mutations (8.00%.4/50;5.19%,4/77) and exon17mutations was showed in3cases (6.00%,3/50;3.90%,3/77).For PDGFRA gene,exon18mutation was detected in4cases (23.53%,4/17;5.19%,4/77) and exon12was found in13cases (76.47%13/17;16.88%,13/77).. There were10wt-GISTs, including six cases of IGF1R positivity in immunochemisty, and of which were detected two cases of the BRAF gene exon15V600E mutations. The statistical analysis showed that, c-KIT or PDGFRA gene mutations just had correlations with tumor locatio (P=0.001,0.002<0.05),genotypes of c-KIT or PDGFRA gene mutations were not related to CD117and DOG1immunohistochemical expression (x2=0.524, P=0.469; x2=0.306, P=0.580; χ2=0.000, P=1.000; Fisher精确概率法诈121, P>0.05), IGF1R’s expression had a significant difference between wt-GISTs ang mutant GISTs (60.00%vs0.00%, P=0.000<0.001). In3cases of CD117-negative GISTs,there were one harboring c-KIT gene exons9A502Y503insAY mutation and the other two having PDGFRA gene exon12V561D mutation. In five DOG1-negative cases/two had c-KIT gene mutation,one had mutation in PDGFRA gene and left ones were wild type.8cases of10wt-GISTs were both positive for CD117and DOG1.ConclusionsResults showed that c-KIT or PDGFRA gene mutations only had direct relations of primary tumor site.There is statistically significant difference between wt-GISTs and mutant GISTs in IGF1R’s expression. Different types of mutations had a certain link to tumors’biological behaviors.For cases harboring PDGFRA gene mutations in our study,the results had some differences from foreign researches,but were similar to domestic studies.For instance.in our study,cases with PDGFRA gene mutations were often high-risk patients, the phenomemon was consistent with some domestic reports but different from foreign studies that showed a benign procedure for those one had PDGFRA gene mutations. The difference may indicate an ethnic difference, while this difference may also lead to different responses to treatments.IGF1R’s immunohistochemical detection can be used as a screening method, alone or combined with other immunohistochemical indicators, prior to analye gene mutations types. Taking into account that the high expression rate of IGF1R in wt-GISTs, it has the possibility of becoming a of GISTs new therapeutic targets, the inhibitor may be used as specific targeted therapies for these patients, thus improving the prognosis of the wt-GISTs.We found two wt-GISTs had the BRAF gene V600E mutation which had been reported could promote tumor cells growth and enhance the anti-apoptotic capacity of tumor cells.Otherwise we found no cases having PIK3CA gene mutation,paying attention its function in other malignant tumors, a further discussion on the matter is still necessary.Further studies in genotype analysis will better individualized treatment schedule for different patients and improve patients’survival and prognosis of GISTs.