Different Mutation Subtypes Of 19del Indicate Distinct Response To EGFR-TKIs Treatment In Advanced Lung Adenocarcinoma

BackgroundLung cancer is one of the malignant tumors with the highest morbidity and mortality worldwide,among which non-small cell lung cancer(NSCLC)accounts for about 85%.With understanding of the potential molecular drivers of NSCLC development and the discovery of targeted oncogenes,rapid progress has been made in the therapy of non-small cell lung cancer.The development of epidermal growth factor receptor(EGFR)tyrosine kinase inhibitors(TKIs)has significantly improved survival rate among advanced NSCLC patients with EGFR mutation.Epidermal growth factor(EGF)and its receptor(EGFR),discovered by Stanley Cohen of Vanderbilt University,are the genes most closely associated with lung adenocarcinoma.Human EGFR gene is located on chromosome 7p11.2,which contains 28 exons,sizing about 200 kb.Tyrosine kinase functional region of receptor is encoded by EGFR exon 18~24.EGFR mutations occur predominantly in non-small cell lung adenocarcinoma patients of Asian origin who have no history of smoking.Compared to patients with negative EGFR mutation,EGFR-mutated patients showed longer progression-free survival(PFS)(11.5 months)and overall survival(OS)(15.4 months).EGFR-mutated NSCLC is a genetically heterogeneous disease including more than 200 distinct mutations.The common mutation loci occur on exons 18-21.Two subtypes of EGFR mutation include exon19 deletion(19del)and L858 R missense mutation on exon 21,are the most common mutations in NSCLC,accounting for 44% and 41% respectively.Both mutations are sensitive to EGFR-TKIs therapy.In addition,studies have shown that after treatment with first-generation EGFR-TKIs,patients with 19 del had longer PFS,comparing with EGFR L858 R mutated patients.What’s more,patients with high mutation abundance were more likely to benefit from EGFR-TKIs than patients with low mutation abundance.Provided the inconsistent effect of EGFR-TKIs on different patients,it is particularly important to screen out these patients who showing a better response to EGFR-TKIs.ObjectiveIn this study,we detected EGFR exon 19 mutation subtypes by next-generation sequencing(NGS).The mutation subtypes were classified according to changed amino acid level resulted of 19 del mutation,and then explored the relationship between clinicopathologic features and corresponding mutation subtypes.The clinical curative effect among each EGFR 19 del subtypes has been analyzed with the expect that EGFR 19 del further classification can indicate the different therapeutic value of the EGFR tyrosine kinase inhibitors.MethodsThis research has been approved by the Henan Cancer Hospital ethics committee.211 patients with EGFR 19 del and L858 R mutations,whom only had a history of EGFR-TKIs treatment,in the department of molecular pathology,Zhengzhou university cancer hospital from 2015 to 2018 were collected.122 patients were followed up through hospital medical records until disease progression or December 2018.The clinicopathological data of the patients were collected and analyzed by chi-square test,and the survival of 19 del and L858 R patients were analyzed.122 patients with EGFR 19 del were then detected by NGS.According to the mutation pattern,we classified the in-frame deletions detected on EGFR exon19 into three groups: codon deletion(CD),with a deletion of one or more original codons;codon substitution and skipping(CSS),with a deletion of one or two nucleotides but the residues could be translated into a new amino acid without changing following amino acid sequence;CD or CSS plus single nucleotide variant(SNV)(CD/CSS+SNV),exclude CD or CSS,there’s another SNV nearby the deletion region.The chi-square test was performed to examine the relationship between the progression status and clinicopathological characteristics of patients with EGFR 19 del.Univariate survival analysis of 122 patients were analyzed by Kaplan-Meier.Independent sample t-test was performed for the mutation abundance of the three mutation subtypes.Clinical data of the three groups were compared by chi-square test,and independent sample t-test was used to compare the missing base number and amino acid number of the mutation subtypes.The Kaplan-Meier survival analysis was used to analyze and draw the survival curve,and Log-rank test was used to compare the survival curves of the three groups.The data of this study were analyzed using SPSS 16.0 statistical software.All P values were 2-sided and P<0.05 was considered statistically significant.Results 1.There was no significant difference in terms of gender,smoking history,family history or stage between EGFR 19 del and L858 R mutations(P>0.05).However,EGFR 19 del is more likely to occur in patients younger than 60 years old(P<0.05).2.The progressive-free survival of EGFR 19 del patients was remarkably higher than that of L858 R patients(P<0.05).3.There was no distinct correlation between the progress status and gender,age,drinking history,family history,TNM stage in patients with EGFR 19del(P>0.05).However,it was related to smoking history(P<0.05).4.Univariate survival analysis was performed on 122 patients,and the results showed that the clinical data did not affect the survival of patients with EGFR 19del(P>0.05).5.There was no obvious difference in the mutation abundance and the clinical data among the three groups(P>0.05).6.The mean number of missing bases in group CD was 14.93,17.2 in group CSS and 14.18 in group CD/CSS+SNV.The results showed significant differences in the number of missing bases between group CD and group CD/CSS+SNV,likewise in group CSS and group CD/CSS+SNV(P<0.05).The mean number of missing amino acids in group CD was 4.98,5.73 in group CSS and 4.76 in group CD/CSS+SNV.Consistently,there were also significant differences in the number of missing amino acids between group CD and group CSS,similarly in group CSS and group CD/CSS+SNV(P<0.05),The CD/CSS+SNV group has the lowest number of missing bases and amino acids.7.The Kaplan-Meier survival analysis was performed on three groups.The median PFS of CD group,CSS group and CD/CSS+SNV group was 11 months,9 months and 14 months,respectively.And it is an obvious difference in PFS between group CSS and group CD/CSS+SNV(P<0.05).the CD/CSS+SNV group has longer PFS.Conclusions 1.EGFR-TKIs have distinct effects on different mutation subtypes of EGFR 19 del in advanced lung adenocarcinoma.2.New molecule subtypes of EGFR 19 del,which is based on changed amino acid level resulted of mutation,is more helpful to clinical prognostic and patients’ therapy.