• Weihua Li, Rui Wan, Lei Guo, Geyun Chang, Dong Jiang, Lin Meng, and Jianming Ying.
• Department of Pathology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, No.17 Panjiayuan Nanli, Beijing, 100021, China. liweihua@cicams.ac.cn.
• Bmc Med. 2022 May 10; 20 (1): 160160.

BackgroundDiverse genomic breakpoints of fusions that localize to intronic, exonic, or intergenic regions have been identified by DNA next-generation sequencing (NGS), but the role of exonic breakpoints remains elusive. We investigated whether exonic-breakpoint fusions could predict matched targeted therapy efficacy in non-small cell lung cancer (NSCLC).MethodsNSCLC samples were analyzed by DNA NGS, RNA NGS, immunohistochemistry (IHC), and fluorescence in situ hybridization.ResultsUsing DNA NGS, kinase fusions were identified in 685 of 7148 (9.6%) NSCLCs, with 74 harboring exonic-breakpoint fusions, mostly anaplastic lymphoma kinase (ALK) fusions. RNA NGS and IHC revealed that 11 of 55 (20%) exonic-breakpoint fusions generated no aberrant transcript/protein, possibly due to open reading frame disruption or different gene transcriptional orientations. Four cases of genomic-positive but RNA/protein-negative fusions were treated with matched targeted therapy, but progressive disease developed within 2 months. Nevertheless, 44 of 55 (80%) exonic-breakpoint fusions produced chimeric transcripts/proteins, possibly owing to various alternative splicing patterns, including exon skipping, alternative splice site selection, and intron retention. Most of these genomic- and RNA/protein-positive fusion cases showed a clinical response to matched targeted therapy. Particularly, there were no differences in objective response rate (P = 0.714) or median progression-free survival (P = 0.500) between intronic-breakpoint (n = 56) and exonic-breakpoint ALK fusion subtypes (n = 11) among ALK RNA/protein-validated patients who received first-line crizotinib.ConclusionsExonic-breakpoint fusions may generate in-frame fusion transcripts/proteins or not, and thus are unreliable for predicting the efficacy of targeted therapy, which highlights the necessity of implementing RNA or protein assays for functional validation in exonic-breakpoint fusion cases.© 2022. The Author(s).

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