The promise of personalized cancer treatment hinges on identifying reliable biomarkers – measurable indicators within the body that can predict how a patient will respond to a specific therapy. For immunotherapy, a powerful approach that harnesses the body’s own immune system to fight cancer, one such biomarker has been tumor mutational burden, or TMB. But inconsistencies in how TMB is measured have hampered its widespread clinical use. Now, a new consensus guideline, developed by experts in China, aims to standardize the process, offering a path toward more dependable and accessible precision oncology.
Immune checkpoint inhibitors have revolutionized treatment for several cancers, but they don’t work for everyone. A key reason is that these drugs rely on the presence of neoantigens – abnormal proteins created by tumor mutations that the immune system can recognize and attack. TMB essentially reflects the number of these potential neoantigens. However, a growing challenge has been the variability in TMB results stemming from differences in sample preparation, the genetic sequencing technologies used and the methods for analyzing the data. This lack of standardization has made it difficult to confidently use TMB to guide treatment decisions.
A Call for Consistent Measurement
The expert consensus, published in Cancer Biology &. Medicine (DOI: 10.20892/j.issn.2095-3941.2025.0351), was developed by the Yangtze River Delta Lung Cancer Cooperation Group (East China LUngcaNcer Group), Youth Committee. It emphasizes that TMB should be treated not as a rough estimate, but as a rigorously controlled clinical measurement. The guidance focuses on improving the reliability and comparability of TMB testing, particularly within the context of immunotherapy for cancer patients in China, though the principles have broader implications.
Central to the recommendations is a focus on sample quality. The consensus stresses the importance of using recently prepared paraffin-embedded tumor tissue – a common method for preserving tissue samples – and ensuring a sufficient amount of tumor cells are present. Validated DNA extraction and quality control procedures are also crucial before sequencing begins. These steps minimize errors and ensure the accuracy of the TMB assessment.
Sequencing and Analysis: Finding the Right Balance
When it comes to actually measuring the mutations, the experts identify whole-exome sequencing – a comprehensive method that sequences all the protein-coding regions of the genome – as the “gold standard.” However, whole-exome sequencing can be expensive and time-consuming. Recognizing this, the consensus acknowledges that targeted panel sequencing – which focuses on a smaller, pre-defined set of genes – is a more practical option for routine clinical use, provided it is carefully validated against whole-exome sequencing results.
To ensure the reliability of targeted panels, the guidance recommends a panel coverage of at least 1.0 Mb (megabase), a sequencing depth of at least 200x – meaning each base in the genome is read 200 times over – and the use of standardized bioinformatics pipelines. These pipelines are essential for accurately removing germline variants (mutations inherited from parents, rather than acquired by the tumor) and reducing biases introduced by the sequencing technology itself. The size of the panel also matters; smaller panels can underestimate TMB, while larger panels more closely reflect the results of whole-exome sequencing.
Beyond “High” vs. “Low”: Context is Key
Perhaps the most significant shift in thinking advocated by the consensus is the move away from simplistic “high” versus “low” TMB cutoffs. The experts argue that TMB values vary dramatically depending on the type of cancer. Clinically meaningful thresholds, should be determined by analyzing actual immunotherapy outcomes in specific cancer types, rather than relying on arbitrary statistical divisions. This nuanced approach recognizes that a TMB value that predicts a good response in lung cancer might not be relevant in breast cancer, for example.
“TMB is no longer just a research concept,” the consensus suggests. “Its value now depends on whether clinicians and laboratories can measure it consistently, interpret it correctly, and place it in the right treatment context.” This means considering not only the TMB score itself, but also the specific assay used, the type of cancer, and the patient’s overall clinical situation.
Implications for Patients and Laboratories
The practical implications of these guidelines are immediate. For oncologists, the consensus provides a clearer framework for deciding when TMB testing might be beneficial, particularly for patients with advanced solid tumors who have exhausted other treatment options. Immunotherapy, as defined by the National Cancer Institute, is a type of cancer treatment that helps your immune system fight cancer. For laboratories, the guidance offers a roadmap for standardizing workflows, from handling specimens to reporting results. This standardization will improve the accuracy and reliability of TMB testing, ultimately benefiting patients.
The development of these guidelines also highlights a broader trend in precision oncology: a shift from simply discovering new biomarkers to making them reproducible, comparable, and clinically interpretable. As the field matures, the focus is increasingly on ensuring that these tools can be reliably integrated into routine clinical practice. If widely adopted, this roadmap could transform TMB from a promising but inconsistent biomarker into a dependable component of personalized cancer care.
Looking ahead, the impact of these standardized guidelines will be closely monitored as more data emerges from clinical practice. Further research will be needed to refine TMB thresholds for different cancer types and to explore the potential of combining TMB with other biomarkers for even more accurate predictions of immunotherapy response. The Chinese Academy of Sciences continues to be a leading force in advancing cancer research and improving patient outcomes.
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