Evolution and genotypic characteristics of small cell lung cancer transformation in non-small cell lung carcinomas

Background:Small cell lung cancer(SCLC)transformation had previously been reported mainly in epidermal growth factor receptor(EGFR)mutant adenocarcinoma.However,the underlying genomic profile remains un-clear.Our study aimed to find the evolution and genotypic characteristic of SCLC transformation.Methods:Thirty-one SCLC transformation patients who were initially diagnosed as non-small cell lung cancer(NSCLC)patients were included.Whole exome sequencing(WES)of both primary and transformed re-biopsy lesions was conducted on 12 patients.Clinical characteristics were analyzed using R software(v.3.6.1).Results:Our study included 31 patients,of whom,three had lung squamous cell carcinoma,6 patients did not carry EGFR mutations,and 30 patients received chemotherapy for SCLCs.The disease control rate(DCR)was 96.7%,and the median progression-free survival(PFS)was 4.03 months.The median time to transformation was 33.07 months,and the median overall survival(OS)was 62.08 months.Somatic mutation analysis showed that besides TP53,RB1,and EGFR,there was a high occurrence of mutations to CSMD3 and ADAMTS19,espe-cially in the EGFR-wild type(EGFR-wt)group.Concerning mutational signature,the EGFR-mutant(EGFR-mut)transformed group favored an apolipoprotein B(APOBEC)mRNA editing catalytic polypeptide-like-associated mutation pattern(P=0.16).DNA damage repair(DDR)-related signatures were significantly enriched in the EGFR-wt transformed group(P=0.034).Additionally,clonal evolution analysis revealed that all patients had the same main trunk genes in the phylogenetic tree.Transformed SCLCs are not sensitive to immunotherapy,possibly due to increased tumor heterogeneity.Conclusions:Our results indicate that the EGFR-wt patients could also transform to SCLCs,but they have different genetic features with EGFR-mut patients.SCLC-transformed patients respond to classical chemotherapy and have a better prognosis than those with classical SCLCs.