The Correlation Analysis Of The Features Of Gene Mutations And The Efficacy Of Targeted Drugs In GISTs

Objective:Most gastrointestinal stromal tumors (GISTs) have the gain-of-function mutations in the c-kit or platelet-drived growth factor a (PDGFRa) gene, which are also the targets of tyrosine kinase inhibitors, Imatinib Mesylate. This study is to analyze the incidence rate, usual mutational situs and types of c-kit and PDGFRa gene in GISTs. Moreover, this article is to study the possible relationship between mutations of c-kit and PDGFRa gene and clinical pathologic characteristics, therapeutic efficacy of imatinib and prognosis.Methods:In partⅠ,30 patients with pathologically confirmed GIST were enrolled in the first Affiliated Hospital of Dalian Medical University from Septemper 2004 to March 2010. Exon 9,11,13 of c-kit gene and exon 12,18 of PDGFRa gene were sequenced by PCR amplification to analyze the characteristics of gene mutations in GISTs. The relationship between the location of primary tumors, size of tumors, histology, mitosis counts, grade of malignant potential and gene mutations were discussed.In partⅡ,15 patients of recurrent or metastatic GIST among 30 cases in partⅠwere treated with imatinib mesylate. The efficacy was evaluated according to Choi evaluation criteria. We analyzed the relationship between gene mutations and the efficacy of imatinib and prognosis. We also discussed the relationship between efficacy of imatinib and the survival. Results:In partⅠ, among 30 cases of GIST,80%(24/30) patients had the mutations of c-kit or PDGFRagene, while the wild type c-kit/PDGFRa GISTs were identified in 20%(6/30) of all cases. C-kit mutations were identified in 79.17%(19/24) of mutation GISTs, while PDGFRamutations were identified in 20.83%(5/24). There were 13 cases with mutations of c-kit exon 11, which was 68.42%of c-kit-mutation GISTs. While there were 6 cases with mutations of c-kit exon 9,31.58%of c-kit-mutation GISTs. C-kit exon 13 and exon 17 were not detected in this study. Among c-kit-mutation GISTs, there were 6 cases of point mutation,6 cases of deletions and 3 cases of insertions and duplications. One case had both point mutation and deletion in c-kit exon 11. The mutations of c-kit exon 11 mostly were clustered in 552-560 at the 5'end of exon 11, and most were point mutations and deletions. All of exon 9-mutations were duplications of GCCTAT in 502-503 of exon 9. PDGFRαmutations included exon 18 mutations (4 cases) and exon 12 mutations (1 case). Most of exon 18-mutations were point mutation-D842V.The results revealed that there were close relationship between gene mutations and tumors location or histology. The overall mutation rate, c-kit gene mutation rate and c-kit exon 11 mutation rate in GISTs originated from stomach were higher than that from small intestinal, colorectal and extra-gastrointestinal tract. The difference was significant (X2=6.771, P=0.034; X2=8.298, P=0.016; X2=6.302, P=0.043). The overall mutation rate, c-kit gene mutation rate and c-kit exon 11 mutation rate were higher in GISTs of spindle cell type than epitheloid and mixed cell type. The difference was significant (X2=7.243, P=0.027; X2=7.304, P=0.026; X2=8.081, P=0.018). However, the mutation rate and different types of mutations had no significant differences between the groups of age, gender, tumor size, location, histology and grade of malignant potential.In partⅡ,15 patients were evaluated for the therapeutic efficacy of imatinib according to Choi evaluation criteria. Among the 15 patients, 80.00%(12/15) patients had mutations, while 20.00%(3/15) patients without mutations.40.00%(6/15) patients had c-kit exon 11 mutation, while 40.00%(6/15) had other mutations. Among the cases with mutations, there were 1 case of CR (8.33%),6 cases of PR (41.67%),5 cases of SD (25.00%),3 cases of PD (25.00%). Among the cases without mutations, there were 1 case of PR (33.33%),2 cases of SD (66.67%), none of CR/PD. Among the patients with exon 11 mutations, there were 1 case of CR (16.67%),3 cases of PR (50.00%),2 cases of SD (33.33%), none of PD. Among the cases with other mutations, there were 2 cases of PR (33.33%),1 case of SD (16.67%),3 cases of SD (50.00%), none of CR. The overall RR of 15 patients was 46.67%(97/15), and the DCR was 80.00%(12/15). There were no significant differences between the mutation group and no-mutation group, also between the exon 11-mutaion group and other-mutation group (P＞0.05).15 patients were evaluated for the toxicities. OnlyⅠ-Ⅱgrade adverse events occurred and were well tolerated and easily controlled.At median follow-up of 28 months, the median TTP was 25 months of mutation GISTs, while 21 months of non-mutation GISTs. The two year PFS rate had no significant differences between the two groups (P＞0.05). However, the two year PFS rate was higher in c-kit exon 11 mutation than others. The difference was significant (X2=6.078, P=0.048). Different types of mutations in two year PFS rate had no significant differences (P＞0.05).Conclusions:1. C-kit gene mutations are the most common type in GISTs. PDGFRa gene mutations are detected in some GISTs without c-kit mutations. C-kit gene mutations mainly concentrate in exon 11. Secondly are c-kit exon 9 mutations. PDGFRagene mutations concentrate in exon 18, secondly are exon 12 mutations. The mutations of c-kit exon 11 mostly are clustered in 552-560 at the 5'end of exon 11, and most common types of mutation are point mutations and deletions. Most c-kit exon 9 mutations are insertions and duplications. The point mutation-D842V is the most common type in PDGFRαexon 18 mutations.2. The mutations of GISTs are closely related to the location of tumors and the histology of GISTs. The rate of c-kit mutation is higher in gastric than that in small intestine,colorectal and extra-gastrointestinal tract. Besides, the rate of c-kit mutation is higher in the spindle cell type of GISTs than that of the epitheloid and mixed-cell type. 3. Imatinib shows significant efficacy in metastatic and recurrent GISTs. We confirm the favorable impact of c-kit exon 11 genotype when compared with other genotypes for patients with advanced GISTs who were treated with imatinib.4. When evaluating the disease of GISTs, Choi evaluation criteria has closer relationship with the further efficacy of imatinib (survival), com-pared with Recist evaluation criteria.