Choosing the Right Genetic Test in Cancer: WGS, WES, and Targeted Sequencing
In this article
Next-generation sequencing (NGS) is a revolutionary technology that enables rapid, sensitive, highly accurate analysis of genetic material. Producing more data in less time than conventional methods, NGS plays a critical role in identifying genetic variants, understanding disease mechanisms, and developing personalized treatments. Particularly in oncology, it provides in-depth insights into cancer's genetic origins and forms the basis of targeted treatment strategies.
In recent years, the dramatic fall in the cost of next-generation sequencing (NGS) has made whole-genome sequencing (WGS) increasingly attractive because it provides extensive genetic information. However, obtaining sufficiently deep sequencing coverage and managing enormous volumes of data remain major obstacles. Target enrichment approaches enable specific subsets of the genome to be isolated through probe hybridization and sequenced, offering lower-cost alternatives to WGS. In particular, when deep sequencing is required, whole-exome sequencing (WES) and customized disease-specific panels balance cost and sensitivity by focusing on the most important genomic regions. However, these targeted approaches risk missing important variants outside the selected regions.
In this article, we examine the advantages and disadvantages of WGS, WES, and targeted sequencing in detail. The right choice largely depends on the research question or clinical problem. Particularly in oncology, selecting these technologies is critical for identifying molecular targets and designing personalized treatments.
Definitions
What Are WGS, WES, and Targeted Sequencing?
- WGS (Whole Genome Sequencing): Sequencing the entire DNA genome, including all coding (exonic) and noncoding (intronic) regions. Because it covers the whole genome, this method provides the broadest and most detailed genetic information.
- WES (Whole Genome Sequencing: Whole Exome Sequencing): Sequences only the exons of protein-coding genes, covering approximately 1% of the genome. Its narrower focus offers advantages over WGS in cost and data analysis.
- Targeted Sequencing: Uses customized panels to sequence particular genes or gene regions. It is especially preferred for investigating specific disease-associated mutations.
Exons and Introns
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Exon: Regions of DNA used to convert genetic information into protein. They are transcribed into RNA and play an active role in protein production. Together, exons form the exome, which is critical for biological functions despite accounting for only 1% of the genome.
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Intron: Gene segments that do not contribute genetic information to protein production and are removed after transcription into RNA. Introns contribute to genetic diversity through roles in gene regulation and alternative exon use.
Comparing WGS, WES, and RNAseq with Targeted Sequencing in Oncology
Targeted therapy is a cornerstone of personalized oncology and aims to clarify the mechanisms of cancer development and resistance pathways. Historically, however, these approaches have produced lower-than-expected success rates. The main reasons include:
- Incomplete or inappropriate panels: For example, adding RNA sequencing to DNA sequencing may increase the target identification rate by 10% or more.
- Lack of evidence and reliance on expert opinion for treatment recommendations: Recommendations based on individual expert opinion rather than international standards are common.
- Mismatch between medicine and target: The medicines used are often inhibitors that are not specific to the target.
- Patients being heavily burdened by prior treatment: Most studies include patients with resistant tumors.
These barriers have been overcome over time, and the following are now more widespread:
- Broader and more appropriate NGS technologies,
- ESCAT, OncoKB and similar actionability scales,
- Greater access to selective medicines, and
- Molecular testing at earlier stages of disease.
The Current NGS Landscape: Where Are We?
Today, targeted NGS is increasingly validated for identifying therapeutic targets, designing personalized treatments, and understanding resistance mechanisms. For example:
- ESMO (the European Society for Medical Oncology) recommends routine NGS for lung cancer, ovarian cancer, prostate cancer, and cholangiocarcinoma as part of routine clinical care.
- SAFIR02-BREAST and similar clinical studies have shown that treatment based on genomic profiling improves progression-free survival in the studied patients.
Comprehensive panel sequencing generally uses panels designed to detect particular genes or mutations. This method enables in-depth examination of specific gene regions (500 to 20000-fold coverage). However, these approaches may be insufficient for detecting large-scale genetic events such as whole-genome duplications, focal copy-number gains, microsatellite instability (MSI), and other such events.
New Horizons with WGS and WES
Advantages of WGS and WES include:
- Greater sensitivity: detection of whole-genome mutational signatures and genomic rearrangements,
- Identification of predisposing variants absent from targeted panels,
- Gene expression profiling of the tumor microenvironment and biomarker detection.
However, implementation presents the following challenges:
- Higher costs and longer analysis times,
- Higher error rates due to low-quality DNA obtained from FFPE samples,
- Stricter tumor purity requirements.
Future Prospects in Oncology
Choosing among NGS technologies depends not only on cost and data volume but also on the clinical context and the research question:
- Targeted NGS is suitable for rapid detection of known variants and deep analysis of selected gene regions.
- WGS and WES are ideal for exploring a broader range of genetic variants and answering research-oriented questions.
- RNAseq is considered the standard for identifying events such as fusion genes and exon skipping.
Broader availability and falling costs will enable WGS and WES to become more widespread. However, integrating them into routine clinical practice will require specialist centers, such as molecular tumor boards, to support patient-centered care.
Conclusion and Commentary
Overall, the right choice among next-generation sequencing (NGS) technologies depends on the clinical context and research needs. WES (whole-exome sequencing) is ideal for rapidly screening a broad range of genetic variants, providing an extensive genetic overview. However, WES generally has lower sensitivity and does not provide the same high resolution as targeted sequencing. Targeted sequencing is considered the gold standard, particularly for somatic or germline oncological investigations, and offers exceptional sensitivity for in-depth analysis of critical gene regions.
For people without a background in genetics, the difference can be explained as follows: WES allows you to scan every book in a library and quickly reproduce it digitally, but you cannot fully analyze the pictures inside the books. Targeted sequencing, by contrast, is like photographing a picture with a high-resolution camera. It preserves clarity even when you enlarge the image. If we think of WES as a 5-megapixel camera, targeted sequencing works like a 100-megapixel camera, providing deeper, clearer, more detailed analysis.
When choosing among NGS technologies, both the high resolution of targeted sequencing and the broader coverage of WES should therefore be considered. Combining these technologies offers a powerful strategy for obtaining a broad genetic perspective while targeting specific variants with high sensitivity.
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