Genomic and transcriptomic features of relapsed small cell lung cancer.
BACKGROUND: Relapsed small cell lung cancer is characterized by treatment resistance and poor outcomes. Genomic and transcriptomic alterations in relapsed SCLC have not been characterized well. We comprehensively profiled relapsed SCLC samples along with patient-matched treatment-naive samples, when available, using whole-exome (WES), whole-genome (WGS), and RNA-sequencing (RNA-seq) to describe the molecular landscape of relapsed SCLC. Our goal is to identify potential novel pathways for additional functional validation and eventually novel therapeutic options. METHODS: We analyzed 54 relapsed and 27 treatment-naive SCLC samples using WES (with 26 patient-matched paired samples). A subset of the samples was also analyzed by WGS (n=28) and RNA-seq (n=31). Differences in mutational signatures, gene expression, structural variants, splicing, and neoantigen profiles at diagnosis and relapse were investigated. RESULTS: Relapsed SCLC samples demonstrated mutation signatures characteristic of platinum and APOBEC mutagenesis. Furthermore, these samples were characterized by MYC, MYCL and MYCN amplifications. Both treatment-naive and relapsed SCLC samples showed high prevalence of mutation-associated neoantigens (median= 86 in treatment-naive and 90 in relapsed SCLC; p=0.8) and TP53 was the most frequently altered gene to result in a neoantigen (48% of analyzed samples). Potential mechanisms of immune evasion, including amplification of CD24, overexpression of IDO1, increased M2 macrophage presence, and upregulation of HLA-E were also observed in relapse samples. Differences in alternative splicing patterns were observed between treatment-naive and relapsed small cell samples. Retained intron events were significantly enriched in treatment-naive samples and affected genes involved in DNA repair, metabolism, and WNT and MYC pathways. CONCLUSIONS: This study highlights the genomic and transcriptomic features of relapsed SCLC. These samples were characterized by genomic instability, WNT and MYC dysregulation, and splicing aberrations. Additional studies targeting the splicing machinery, WNT signaling, and immune evasion pathways could identify novel therapeutic vulnerabilities in SCLC.