Background: NUT midline carcinoma (NMC) is a rare aggressive malignancy often occurring in the tissues of midline anatomical structures. Except for the pathognomonic BRD3/4−NUT rearrangement, the comprehensive landscape of genomic alterations in NMCs has been unexplored.
Patients and Methods: We investigated three NMC cases, including two newly diagnosed NMC patients in Seoul National University Hospital, and a previously reported cell line (Ty-82). Whole-genome and transcriptome sequencing were performed for these cases, and findings were validated by multiplex fluorescence in situ hybridization and using individual fluorescence probes.
Results: Here we present the first integrative analysis of whole-genome sequencing, transcriptome sequencing and cytogenetic characterization of NUT midline carcinomas. By whole-genome sequencing, we identified a remarkably similar pattern of highly complex genomic rearrangements (previously denominated as chromoplexy) involving the BRD3/4−NUT oncogenic rearrangements in two newly diagnosed NMC cases. Transcriptome sequencing revealed that these complex rearrangements were transcribed as very simple BRD3/4−NUT fusion transcripts. In Ty-82 cells, we also identified a complex genomic rearrangement involving the BRD4−NUT rearrangement underlying the simple t(15;19) karyotype. Careful inspections of rearrangement breakpoints indicated that these rearrangements were likely attributable to single catastrophic events. Although the NMC genomes had >3,000 somatic point mutations, canonical oncogenes or tumor suppressor genes were rarely affected, indicating that they were largely passenger events. Mutational signature analysis showed predominant molecular clock-like signatures in all three cases (accounting for 54 − 75% of all base substitutions), suggesting that NMCs may arise from actively proliferating normal cells.
Conclusion: Taken together, our findings suggest that a single catastrophic event in proliferating normal cells could be sufficient for neoplastic transformation into NMCs.