Tumor Mutational Burden (TMB)

TMB is a measure of the number of mutations carried by tumor cells. Tumors with many mutations have a high mutational burden (high TMB). Many of the tumors with high TMB are also MSI-H or microsatellite instability high. Approximately 3% of tumors classified as MSS (microsatellite stable) also have high TMB. TMB is currently used as a predictive biomarker for immune checkpoint inhibitors.

TMB is measured in stage IV, metastatic colorectal (mCRC) tumor biopsies as part of comprehensive biomarker panel using NGS (next generation sequencing). TMB status cannot currently be tested independent of a comprehensive biomarker panel.

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 currently used as a predictive biomarker for a possible response to immunotherapy mostly in MSI-H tumors and in high TMB MSS tumors. Pembrolizumab is FDA approved for high TMB MSS tumors.

The comprehensive biomarker panel can identify multiple biomarkers that are actionable (there are drugs available). Discuss with your doctor the results of your biomarker testing and treatment options based on your tumor profile.

Every treatment has the potential to cause some side effects. Some people may be more sensitive than others to a drug. The response to a specific treatment also depends on your medications, vitamins, and herbal supplements.

Tell your doctor and pharmacist about all your medications, vitamins, and treatments. If you are experiencing severe side effects, call your doctor immediately.

For more on side effects of other chemotherapy regimens, click here.