KIT/PDGFRA Mutation And Dystrophin Expression In Gastrointestinal Stromal Tumor And Prognosis Analysis

OBJECTIVES:To investigate the relationship between the type of KIT/PDGFRA gene mutation and Dystrophin expression and the clinicopathological features of gastrointestinal stromal tumor（GIST）.To explore the value of two factors above mentioned in evaluating the prognosis of GIST patients with current therapy including surgery and imatinib,and to find more accurate indicators to judge the biological behavior and prognosis of GIST.And to investigate the clinicopathological characteristics,diagnostic clues,and prognoses of multiple sporadic GISTs.METHODS:（1）A total of 1,163 patients diagnosed with GISTs between January 2006and December 2018 were enrolled in this study.Mutation analysis was performed for exons 9,11,13,and 17 of KIT and exons 12 and 18 of PDGFRA.Mutations were grouped into 12 categories according to the gene,exon,and involved codons;they were analyzed considering the clinical characteristics,disease-free survival（DFS）,and overall survival（OS）of patients with GISTs.（2）A total of 291 cases of GIST samples were collected between January 2002 to December 2012.The Dystrophin expression was detected by immunohistochemistry,and the relationship between Dystrophin expression and clinical pathological characteristics and prognosis of GIST was analyzed.（3）Twenty-seven patients with multiple sporadic GISTs and 11 patients with metastatic GISTs mimicking sporadic GISTs were analyzed.The clinicopathological characteristics,genetic mutation types,and prognoses were summarized.In addition,1066 cases of primary GISTs with a single lesion diagnosed at the same hospital were included as controls.RESULTS:（1）We classified the gene mutation types into the following 12 categories:wild-type;PDGFRA mutations;KIT exon 9 mutations;KIT exon 13 mutations;KIT exon 17 mutations;KIT exon 11 homozygous mutations;KIT heterozygous intron10/exon 11 junction deletions（involving codons 550-558）;other heterozygous KIT exon 11 deletions involving codon 557 or 558;other heterozygous KIT exon 11deletions only involving one codon,excluding codon 557 and 558;other heterozygous KIT exon 11 deletions involving two or more codons,excluding codons 557 and 558;and KIT exon 11 heterozygous substitutions and duplications.When we compared the proportions of the 12 different genotypes of GISTs in the high-risk（according to modified NIH or AFIP scheme）and metastatic groups,we found that they could be reclassified into the following three groups:Group 1:KIT exon11 homozygous mutations and KIT heterozygous intron 10/exon 11 junction deletions（involving codons 550-558）;Group 2:other heterozygous KIT mutations,including exon 9duplications,exon 11 deletions involving codons 557 and/or 558,and deletions involving two or more codons,excluding codons 557 and/or 558;and Group 3:other heterozygous KIT exon 11 mutations,including deletions involving only one codon,excluding codon 557 and 558;substitutions and duplications;KIT exon 13 and 17mutations;PDGFRA mutations and the wild-type.Group 1 was the most common among high-risk and metastatic GISTs,whereas group 3 was observed in low-risk GISTs.The proportion of group 2 was between that of groups 1 and 3 in high-risk and metastatic GISTs.Pairwise comparisons among the three groups showed significant differences（P<0.001）.In low-risk GISTs,we identified two predictors of worse DFS:tumor origin in the rectum and KIT exon 11 deletion involving two or more codons.In high-risk GISTs treated with R₀ resection and imatinib,patients with KIT exon 11homozygous mutations and KIT intron 10/exon 11 junction deletions demonstrated the highest recurrence rate,indicating that these mutations can be independent prognostic factors of DFS（P<0.001）.The presence of KIT exon 11 homozygous mutations also independently influenced OS（P=0.041）.（2）Of the 291 cases of GIST,234 showed positive expression of Dystrophin,including 31 strong positive expression and 203weak positive expression,and 57 showed negative expression of Dystrophin.In GIST tumors of very low risk,low risk,intermediate risk and high risk,the rate of Dystrophin negative expression was 5.3%,7.4%,11.1%and 27.4%,respectively.Loss of Dystrophin expression was significantly associated with increased risk of GIST（P<0.001）.In the metastatic GIST at the time of initial diagnosis,the rate of negative Dystrophin expression was as high as 81.3%.Negative Dystrophin expression was related to tumor metastasis,with statistical significance（P<0.001）.（3）Compared with1066 cases of primary GIST with a single lesion,multiple sporadic GISTs occurred at an older age,were more common in women than in men,and were located mainly in the stomach.They were generally small in size,had a low mitotic index and were more often rated as very low risk/low risk（All of P<0.001）.Mutation analysis of all available lesions revealed different KIT/PDGFRA mutation patterns among tumors from the same patients.No patient relapsed during the follow-up period.Among 11 patients with metastatic GISTs that mimicked multiple sporadic GISTs,multiple lesions from the same patient always had concordant pathological and mutational characteristics;namely,they carried an identical KIT/PDGFRA mutation,and the mitotic index was usually high.CONCLUSIONS:（1）Further subdivision of KIT and PDGFRA gene mutation types is of certain value in evaluating the prognosis of GIST patients low-incidence mutations such as KIT exon 11 homozygous mutations or intron 10/exon 11 junction deletions in GISTs（4.1%and 1.3%,respectively）should be carefully evaluated to explore novel treatment strategies,as tumors with these mutations have a high recurrence rate and a very poor prognosis after surgery followed by imatinib adjuvant treatment.（2）Loss of Dystrophin expression is closely related to the metastasis of GIST,and it can be used as a prognostic marker for high-risk GIST patients underwent complete surgical resection and imatinib adjuvant therapy.（3）The multiple sporadic GISTs are rare.The prognoses of patients with multiple sporadic GISTs are not worse than those of patients with a single lesion of the same risk under the same treatment.It is suggested that multiple tumor lesions in the same patient may not increase the risk of tumor recurrence.When it was difficult to distinguish multiple sporadic GISTs from metastatic GISTs,multiple lesions in the same patient carried different KIT/PDGFRA mutation patterns,which supported tumor multiplicity,while the concordant hypermitotic phase in multiple lesions of GISTs suggested that the tumor was metastatic.