TMB(WES) - CB-Gene

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TMB(WES) Testing Services

In the era of precision medicine, cancer immunotherapy, particularly the use of immune checkpoint inhibitors (ICIs), has revolutionized the treatment landscape for various cancers. However, not all patients benefit equally from treatment, making the identification of biomarkers that can accurately predict efficacy crucial. Tumor mutational burden (TMB) has become a highly sought-after metric, and whole-exome sequencing (WES) is considered the gold standard for measuring TMB.

Definition

Tumor mutational burden (TMB) refers to the total number of somatic gene mutations (including point mutations, insertions/deletions, etc.) per million base pairs in a tumor genome. It quantifies the degree of mutation in tumor cells.

Simply put, a higher TMB indicates a higher number of abnormal proteins (neoantigens) produced by tumor cells. These neoantigens are more likely to be recognized as "foreign" by the body's own immune system (T cells), triggering a more robust immune attack. When immunotherapies such as PD-1/PD-L1 inhibitors are used to remove tumor suppression of immune cells, patients with high TMB tumors are more likely to achieve favorable treatment outcomes and durable clinical responses.

Principles

WES technology relies on high-throughput sequencing of all approximately 20,000 protein-coding exons in the human genome (approximately 1% of the entire genome). By comparing the gene sequences of tumor tissue with those of the patient's own normal tissue (typically blood or adjacent tissue), bioinformatics algorithms can accurately identify somatic mutations that occur only in tumor cells.

The formula for calculating TMB is:
TMB = (Total number of somatic mutations detected / Total size of exon region covered by sequencing (Mb))
The unit is mut/Mb (mutations per million bases).

For example, if a WES test covering 35Mb of exon region identifies 350 somatic mutations in a sample, the TMB value is 350 / 35 = 10 mut/Mb.

WES-TMB Testing Workflow

Sample Collection and Preparation

Tumor tissue (formalin-fixed paraffin-embedded sections or fresh-frozen tissue) and paired normal tissue (usually peripheral blood) are collected from the patient.

DNA Extraction and Quality Assurance

High-quality genomic DNA is extracted from the sample and tested for concentration and integrity.

Library Construction and Capture

DNA is fragmented, sequencing libraries are constructed, and probe hybridization is used to enrich for whole-exome regions.

High-Throughput Sequencing

Paired-end sequencing is performed on high-throughput sequencing platforms such as Illumina or MGI to ensure sufficient sequencing depth (typically >100x) to ensure detection accuracy and sensitivity.

Bioinformatics Analysis

* Sequence Alignment: Sequencing reads are aligned to the human reference genome.

* Variant Calling: Somatic single nucleotide variants (SNVs) and small insertion/deletions (InDels) are identified by comparing sequences between tumor and normal samples.

*Filtering and Annotation: Filters out germline mutations and sequencing errors, and functionally annotates the remaining somatic mutations.

*TMB Calculation: The accurate TMB value is ultimately calculated using the formula above.

Reporting and Interpretation

A comprehensive report containing information such as the TMB value, mutation profile, and key driver gene mutations is generated and clinically interpreted by a professional team to inform physicians' medication decisions.

Advantages

Compared to currently commonly used targeted sequencing panels (large panels), WES offers irreplaceable advantages:

"Gold Standard" and Unbiasedness

WES covers the entire exome, exceeding the detection range of any other panel. It unbiasedly captures all coding region mutations, maximally reproducing the true TMB value, and avoiding TMB calculation bias caused by panel design variations (e.g., varying number of genes or size).

Data Traceability and Secondary Analysis Value

The data generated by a single WES test is a valuable asset for patients. With the advancement of scientific research, new biomarkers are constantly being discovered. Existing WES data can be reanalyzed at any time to uncover new clinical value without the need for retesting.

Outstanding Scientific Value

The comprehensive data provided by WES is a powerful tool for discovering new pathogenic genes, new drug targets, and new antigens, significantly advancing both basic oncology research and translational medicine.

In summary, WES-based TMB testing services represent the current state-of-the-art in tumor genomic analysis. Not only does it provide the most reliable basis for the precise application of immunotherapy in clinical practice, avoiding misdiagnosis and wasted medical resources, but it also opens the door to understanding tumor heterogeneity and evolutionary mechanisms at the research level. Despite its relatively high cost and analytical complexity, with the continuous decline in sequencing technology prices and the increasing sophistication of bioinformatics tools, WES is gradually moving from research to the clinic, becoming a core component of high-end precision medicine services, bringing new hope to more cancer patients.

Application Scenarios

Predicting Immunotherapy Efficacy: This is the core application of WES-TMB testing. The FDA has approved TMB-based companion diagnostics (such as those based on large NGS panels) for selecting patients with solid tumors for treatment with pembrolizumab (K-12). A high TMB (generally defined as ≥10 mut/Mb) is a key inclusion criterion.

Patient Screening for Clinical Trials: In many clinical trials involving new immunotherapies, a high TMB is a key biomarker for enrollment, helping to enrich the potential responder population and improve trial success rates.

Panoramic Tumor Genome Analysis: WES not only provides TMB but also simultaneously detects driver gene mutations, copy number variations, microsatellite instability (MSI), and other indicators across all coding regions, providing patients with the most comprehensive genomic profile possible, guiding targeted therapy, chemotherapy, and genetic risk assessment.

Research on Rare Cancers or Complex Cases: For difficult cases where the cancer type is unknown and standard testing fails to provide guidance, WES-TMB testing can provide breakthrough diagnostic and treatment clues.

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Email: sales@cobioer.com

Definition

Principles

"Gold Standard" and Unbiasedness

Data Traceability and Secondary Analysis Value

Outstanding Scientific Value

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