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  O18 - Cancer Control and Epidemiology II (ID 133)

  • Event: WCLC 2013
  • Type: Oral Abstract Session
  • Track: Prevention & Epidemiology
  • Presentations: 1
  • Moderators:M.R. Spitz, L. Irving
  • Coordinates: 10/29/2013, 10:30 - 12:00, Bayside 103, Level 1

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    O18.01 - Multi-'omic analysis of an arsenic-associated lung squamous cell carcinoma reveals specific DNA level signatures (ID 283)

    10:30 - 10:40  |  Author(s): L. Gil
    • Abstract
    • Presentation
    • Slides

    Background
    Chronic low-level exposure to arsenic is an emerging cancer risk factor in many parts of the world, including North America. The lung is one anatomical site prominently affected by the carcinogenic effects of arsenic, evident by the striking incidence of lung cancer in never smokers with chronic exposure. Histologically, arsenic related lung tumors are indistinguishable from those induced by other lung carcinogens, and molecularly, arsenic specific DNA copy-number, methylation and expression changes have been identified. Arsenic mediated carcinogenesis occurs through a combination of molecular mechanisms; however, high resolution, multi-'omic analyses of arsenic related tumors have been difficult due to the lack of fresh frozen samples required to obtain high quality DNA and RNA. In this study, we sought to characterize global changes in DNA sequence and methylation levels and their impacts on gene expression in a lung tumor from a patient with chronic arsenic exposure (As-LUSC).

    Methods
    Tumor and non-malignant lung tissues were obtained from a never smoker with lung squamous cell carcinoma (LUSC) who had no family history of lung cancer and 50 years of chronic exposure to high levels of arsenic-contaminated drinking water. Whole genome sequencing was performed and the tumor's mutational signature was compared to those observed in 194 previously characterized NSCLC tumors from the cancer genome atlas (TCGA). DNA methylation was measured using high density methylation arrays and gene expression by RNA sequencing.

    Results
    The As-LUSC exhibited alterations typical of LUSC, such as copy number gains at 3q26 (SOX2 locus) and expression of squamous markers including up-regulation of KRT6B, DSG3, MMP12, KRT5, and down-regulation of PDK4, which are consistent with LUSC histology. However, the As-LUSC harbored a low number of point mutations (only 49 non-synonymous mutations affecting coding DNA sequences) and had a remarkably high fraction of T>G/A>C and low fraction of C>A/G>T transversions, which are features uncharacteristic of LUSCs that suggest arsenic is associated with a distinct mutational spectrum. Furthermore, at the gene level, we identified a G>C mutation in TP53 which is rare in lung tumors (<0.2%) but has been observed in other arsenic-related malignancies. Clustering analysis using ~450,000 methylation probes revealed that the As-LUSC methylation profile was completely distinct from never smoker LUSCs from the TCGA. Of interest, the As-LUSC exhibited lower levels of methylation at CpG islands sores that are not associated with genes, although have been described to exhibit cell type specific methylation patterns.

    Conclusion
    By applying whole genome sequencing, methylation and expression profiling of a LUSC from a never-smoker patient chronically exposed to arsenic, we identified a distinct mutational spectrum and methylation pattern in the As-LUSC. Our results support the concept that arsenic induces lung cancers through mechanisms different from tobacco smoke and other carcinogens. Further study of the mutational profiles of additional arsenic-related cancers is warranted and may yield valuable insight into arsenic associated tumourigenesis, leading to the development of novel diagnostic and therapeutic targets for environmental monitoring and treatment.

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