Tumor Mutational Burden (TMB)
What is the TMB biomarker?
TMB is a biomarker that is not linked to a mutation in a specific gene. Instead, TMB is a measure of the overall mutations found in the DNA of cancer cells. Tumors with many mutations have high mutational burden (high-TMB). Many of the tumors with high-TMB also have characteristics of high microsatellite instability (MSI-H). However, about 10% of tumors classified as MSS (microsatellite stable) also have high-TMB with a high mutational burden.
What does TMB biomarker mean?
When and how should I have TMB biomarker testing?
TMB is measured only in stage IV, metastatic colorectal cancer patients (mCRC) who had a sample of their tumor (biopsy) sent for comprehensive biomarker testing by NGS (next generation sequencing) using a multi-gene panel. TMB status cannot be identified through testing for mutations in just a few genes at one time.
If a colorectal tumor cannot be removed by surgery or there is not enough tumor tissue for biomarker testing, ask your doctor about using a blood sample (liquid biopsy) for biomarker testing and TMB.
What do I do with this information?
Currently, there are no standard recommendations for measuring TMB. Results from several clinical trials suggest that tumors with high-TMB respond well to immunotherapy with checkpoint inhibitors such as pembrolizumab, nivolumab, and ipilimumab. Therefore, high-TMB is a predictive biomarker for good response to immunotherapy.
The multi-gene panel testing could be useful in identifying multiple biomarkers. Discuss with your doctor the results of your biomarker testing and suitable treatment options for your tumor profile.
What are the potential side effects?
Every treatment has the potential to cause some side effects. Some people may be more sensitive than others to a particular drug. It also depends on your other treatments, medications, vitamins and herbal supplements. For example, side effects could be worse if you are treated with radiation at the same time. Your cancer drugs may also interact with vitamins and herbal supplements, which means it is dangerous to take them together. Tell your doctor and pharmacist about all of your medications, vitamins, and treatments. Call your doctor immediately if you are experiencing severe symptoms.
For more on side effects of other chemotherapy regimens, click here.
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