Both lung squamous cell carcinoma (LUSC) and lung cancer with neuroendocrine features (LUNE; i.e., small cell carcinoma (SCLC), large cell carcinoma (LCNEC) and other subtypes) are associated with tobacco smoking and have a very poor prognosis. We sought to characterize their clonal architecture and illustrate how the evolutionary patterns differ across these lung cancer subtypes. We performed multi-region whole genome sequencing of 83 samples from 36 LUSC and 67 samples from 23 LUNE patients that had been resected before systemic therapy.
Among somatic copy number alterations, we observed genome doubling intra-tumor heterogeneity (ITH) and massive genomic instability in both subtypes. For somatic nucleotide variants (SNVs), the total mutation burden was higher in LUSC (16.7 average number of mutations/Mb) than LUNE (12.7/Mb), but for SNVs ITH was higher in LUNE. Among driver genes, TP53, CDKN2A, CR1, and NRK in LUSC and TP53, KRAS, KMT2D, and RB1 in LUNE were frequently mutated and were always clonal. Evidence of positive selection was found for TP53, PTEN, KMT2D and KEAP1 in LUSC, and for TP53 and KRAS in LUNE. As expected, the dominant mutation signatures in LUSC clones included signatures 4, 1, and 5, while APOBEC signatures (2 and 13) were predominantly found in sub-clones. In contrast, no evidence of APOBEC signatures were found in LUNE. Among structural variants, LUNE had more events (339.25 average number of events/tumor) than LUSC (206.7/tumor), with considerable ITH in both subtypes, particularly in LUNE. In LUNE, the dominant mechanism responsible for SVs included fork stalling and template switching within the microhomology-mediated break-induced repair (MMBIR). We found recurrent fusion events with hotspots including those previously identified near TTC28/CHEK2 (42% LUSC and 35% LUNE) and LRP1B (42% LUSC). Additional hotspots were found in chromosome bands 20p12.1 (22% LUSC), 1p31.1 (19% LUSC) and 12p11.22 (22% LUNE). We found >10-fold higher transposon insertions (LINE1) in LUSC (71.9 average number of events/tumor) than LUNE (6.3/tumor). Our findings improve our evolutionary understanding of these lung cancer subtypes and warrant further investigations on the mechanisms involved in clonal genomic instability.
Citation Format: Tongwu Zhang, Joshua Sampson, Pier Alberto Bertazzi, Angela Pesatori, Dario Consonni, Bin Zhu, Belynda Hicks, Xing Hua, Jianxin Shi, Kevin Brown, Stephen Chanock, Maria Teresa Landi. Comparison of intra-tumor heterogeneity and clonal evolution across lung cancer subtypes by multi-region whole genome sequencing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1187.