Breadth versus depth: whole transcriptome sequencing has reduced sensitivity for detection of clinically relevant fusions compared to RNA comprehensive genomic profiling.

While there is great potential for unbiased next-generation sequencing (NGS) approaches-eg, whole transcriptome sequencing (WTS)-for exploration, discovery, and clinical application in the realm of oncology, there are limitations that should be considered when relying on these methodologies for clinical decision making. When using WTS for the detection of clinically relevant gene fusions in tumor specimens, a key consideration is whether a limited coverage depth (approximately 30-50X) is sufficient for detecting these events, especially in samples with low tumor purity. We demonstrate the reduced sensitivity of both a commercial WTS assay for the detection of clinically relevant fusions in analytical validation control samples and of a research use only (RUO) WTS assay for the detection of clinically relevant fusions in real-world clinical samples compared to RNA comprehensive genomic profiling (CGP). Notably, the RUO WTS assay would not have reported 30% (6/20) of fusions detected using RNA CGP assays in fusion-positive tumor samples, highlighting a potential disadvantage of broader sequencing.