Targeted next-generation sequencing of DNA has become more widely used in the management of patients with lung adenocarcinoma; however, no clear mitogenic driver alteration is found in some cases. Researchers at Memorial Sloan Kettering Cancer Center evaluated the incremental benefit of targeted RNA sequencing (RNAseq) in the identification of gene fusions and MET exon 14 (METex14) alterations in DNA sequencing (DNAseq) driver-negative lung cancers.
Lung cancers driver negative by MSK-IMPACT underwent further analysis using a custom RNAseq panel (MSK-Fusion). Tumor mutation burden (TMB) was assessed as a potential prioritization criterion for targeted RNAseq.
As part of prospective clinical genomic testing, the researchers profiled 2,522 lung adenocarcinomas using MSK-IMPACT, which identified 195 (7.7%) fusions and 119 (4.7%) METex14 alterations. Among 275 driver-negative cases with available tissue, 254 (92%) had sufficient material for RNAseq. A previously undetected alteration was identified in 14% (36/254) of cases, 33 of which were actionable (27 in-frame fusions, 6 METex14). Of these 33 patients, 10 then received matched targeted therapy, which achieved clinical benefit in 8 (80%). In the 32% (81/254) of DNAseq driver-negative cases with low TMB [0-5 mutations/Megabase (mut/Mb)], 25 (31%) were positive for previously undetected gene fusions on RNAseq, whereas, in 151 cases with TMB >5 mut/Mb, only 7% were positive for fusions (P < 0.0001).
Analysis of Clinical Benefit
RNAseq-based matched therapy for 10 of 33 patients whose tumors were found to be positive for targetable gene fusions (9) or METex14 (1). Eight of the 10 patients showed clinical benefit. The three alterations deemed not targetable were the HDAC5-PIK3CA and YWHAE-SMYD4 fusions, and EGFRvIII. PD, progression of disease; PR, partial response; SD, stable disease. *, Response assessment by RECIST version 1.1. **, Confirmed PR.
Targeted RNAseq assays should be used in all cases that appear driver negative by DNAseq assays to ensure comprehensive detection of actionable gene rearrangements. Furthermore, we observed a significant enrichment for fusions in DNAseq driver-negative samples with low TMB, supporting the prioritization of such cases for additional RNAseq.