| BackgroundIn 2015,there were a total of 4.29 million new cancer cases and 2.81millioin cancer deaths in China.Lung cancer has the highest incidence and mortality in a variety of different types of cancer.With its rapid increase in morbidity and mortality,lung cancer has become the most harmful malignant tumor to human health.One of the main causes of the highest incidence of lung cancer is smoking,in addition,environmental pollution has also played a certain role.The carcinogenic effect of smoking is mainly reflected in the male population,while in female patients,gene mutations mainly accounted for carcinogenesis.According to the classification by WHO,lung cancer was divided into non-small-cell lung cancer(NSCLC)and small-cell lung cancer(SCLC)on the basis of treatment effect,prognosis and biological properties.Among them,NSCLC accounts for about 85%of lung cancer histologies,and SCLC about 15%.In NSCLC,lung adenocarcinoma accounted for about 50%.Due to the different aspects,lung adenocarcinoma and small-cell lung cancer are usually treated individually.First,lung adenocarcinoma originated from alveolar epithelial cells,while small-cell lung cancer originated from neuroendocrine cells;Second.the biological behaviors between lung adenocarcinoma and SCLC aredifferent,Compared to adenocarcinoma,SCLC is prone to early metastases.Finally,the treatment options for SCLC areless than adenocarcinoma,and the 5-year survival rate of SCLC is only about 6%.With the recent studies on the pathogenesis of lung cancer,the drivergenes and the corresponding targeted therapy are gradually applied toclinical practice.Driver gene is a genetic abnormality that can lead to the occurrence and development of malignancy.The treatment of abnormal genes can effectively prolong the survival of patients.The discoveryof EGFR and ALK genes have made the treatment of advanced lung cancer more individualized.Patients with EGFR sensitive mutation treatedwith TKI can achieve approximately 12 months in progression free survival(progression-free survival,PFS).Through rebiospy of patients after resistance to TKI,researchers found that 50%drug resistance is caused byEGFR20 exon T790M mutations,the MET amplification andPIK3CA mutations also account fora certain proportion;the concern is that drug resistance in 5%-15%is due to the presence of a pathological transformation,namely SCLC transformation.Transformation of adenocarcinoma to small-cell lung carcinoma(SCLC),both components harboring similar EGFR alterations after failure of EGFR blockade with specific tyrosine kinase inhibitors(TKIs),was firstly reported by Zakowski et al.and echoed by many other authors worldwide.There are 3 common points in this phenomenon:first,the EGFR mutation in baseline adenocarcinoma and transformed SCLC stays the same;second,the PFS and OS to TKI of transformed SCLC patients is similar to other patients;third,transformed SCLC showed good efficacy to chemotherapy.Despite the small-cell transformation phenomenon,it is not enough to draw a conclusion that such transformationcaused TKI resistance.Some SCLC patients withEGFR sensitive mutationalso has a good efficacywithTKI.At present,there hasbeen no sufficient research to confirm the clinical features and molecular mechanismof this phenomenon of transformation from adenocarcinoma to SCLC.The purpose of this study was to explore the clinical features and molecular mechanism of this kind of transformation to provide hintsfor clinical strategies of treatment for such patients.Chapter 1 The clinical features of transformation from adenocarcinoma to SCLCObjectiveTo investigate the clinical features of transformation from adenocarcinoma to SCLC.MethodsScreening SCLC transformed patients among those with EGFR-TKI failure between 2004 and 2014 for the study.All the patients had written informed consent for the genetic analysis.The inclusion criteria were as follows:1)Histologically confirmed lung adenocarcinoma before TKI.2)EGFR mutation was detected by sequencing or ARMS(amplification resistance mutation system)before treatment.3)Underwent rebiospy and confirmed to have both SCLC transformation and EGFR-TKI resistance.4)Detailed clinical information of patients was available for assessment of tumor response and survival analyses.All analyses were done with SPSS 22.0 software,Chi-square test(Kappa)was used to detect the clinical parameters and response to TKI.Survival analyses were performed by Kaplan-Meier.All statistical tests were two-sided and P<0.05 was deemed to be statistically significant.Results1.The clinical features of patients with small-cell transformationA total of 15patients developed SCLC transformation after resistance to EGFR-TKI.The median age of patients was 53 years,most of the patients aged<60 years(86.87%),non smokers(76.4%),93.3%(14/15)of small-cell transformation phenomenon occurred in patients with EGFR exon 19 deletion.Compared with non-transformed patients,age,gender,smoking history,ECOG PS score and other clinical factors were well balanced,and the difference was not statistically significant.2.The efficacyof EGFR-TKI and prognosis in small-cell transformed patients.In this study,the patients with small-cell lung cancer transformation accounted for 6%(15/233)among all patients with TKI resistance.The disease control rate(DCR)and objective response rate(ORR)of these patients treated with TKI were93.3%and 73.3%,respectively.We divided the 233 patients into two groups according to the presence of SCLC transformation and compared the efficacy of TKI and PFS between groups,and the results showed no significant difference(P=0.275;P=0.997).The survival analyses demonsrated thatthe median PFS and OS of these patients were11.7months(95%CI,8.9-14.4)and 29.4 months(95%CI,23.8-35.0)respectively.Compared with non-transformed patients,there was no significant difference(P=0.275,P=0.997).3.The response to chemotherapy regimens in SCLC transformed patients11 out of 15 patients received etoposide + cisplatin/irinotecan plus cisplatin after transformation,the ORR and DCR were 27.3%and 66.7%,respectively,and the median PFS was 3.3 months.Conclusion1.Small-cell transformation was commonly seenin young,non-smoking patients with EGFR exon 19 deletion,no significant differences in clinical features were found compared to non-transformed patients.2.The efficacy of TKI and overall survival in SCLC transformed patients was similar to non-transformed patients.3.The response to chemotherapy was poor in SCLC-transformed patients.Chapter 2 Genetic abnormalities during transformation to SCLCObjectiveTo explore the genetic abnormalities during transformation to SCLC.MethodsPatients enrolled in section one were analysed.15 patients were confirmed to develop SCLC-transformation.The inclusion criteria were sufficientpre-and post-transformation tumor tissues available for next-generation sequencing(NGS).Three paired tumor tissue samples underwent NGS for 295 genes to detect genetic abnormalities with the depth of 1000X.Results1.The gene mutations in pre-and post-transformation tissue samples.All 4 patients harbored EGFR and TP53 mutation at the baseline and after transformationinto small-cell lung cancer.Emerged and disappeared mutations in a fewpatients.2.The mutation abundance of TP53 and RBI rose from 20%to 80%after transfromation.2.The gene copy number variation in post-transformation patients.Two out of 4 patients gained increased DAXX,NOTCH4 and CUL4A gene copy numbers.The copy numbers of EGFR increased in all 1 patient after transformation to SCLC.Conclusion1.Loss of heterozygosity of TP53and RBI may contribute to the SCLC transformation.2.Gained gene copy numbers mightcontribute to this kind of transformation.Chapter 3 The molecular mechanisms that contribute to TKI resistanceduring SCLC transformation.ObjectiveTo explore the molecular mechanisms that contribute to TKI resistanceduring SCLC transformation.MethodsAll the 15 patients with SCLC transformation were enrolled for this section.The inclusion criteria were as followsaccording to the detection method used.1)For patients with tumor tissue samples after transformation,DNA extraction and EGFR sequencing wereperformed.2)The EGFR expression level was detected in the matchedsampleswith both pre-and post-transformation tumor tissue.3)Six matched and 5 post-transformationplasma tumor DNA underwent NGS for 168 geneswiththe depth of 10000X to explore the mechanism of resistance to TKI.Results1.EGFR expression in two pairs of matched samples wasdetected.The expression of EGFR in both pre-transformation samples were at high level,while they werenegative in post-transformation samples.2.The EGFR mutation status of post-transformation samples keep the same as thebaseline.3.The NGS result on plasma from 3 post-transformation patient showed an EGFR T790M mutation,which was not found in the pre-transformation tissue sample from the same patient.ConclusionThe mechanisms of acquired resistance to TKI during SCLC-transformation mightinclude two parts:the emergence of classic drug resistance mutations such as low-abundance T790M undetectable due to the intra-tumor heterogeneity and the downregulationof EGFR expression. |
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