Last updated – 14 June 2021

What does Tumor Mutation Burden ‘TMB’ mean to me?

This is the total number of mutations (DNA mistakes) that are found within a specific measured area of your tissue sample (biopsy) ie the density or burden of cancerous mutations. This is measurement is described as “mutations per megabase.” (muts/mb). Knowing the TMB score (tumor mutational burden) in your biopsy sample can help your medical team plan the most effective treatment plan.

Tumor mutational burden is a type of biomarker called TMB.

In recent times it has been acknowledged that tumors that record a higher TMB score respond better to certain types of immunotherapy ( ie Check Point Inhibitors)  [Source/Origin]

What does this TMB Score mean to me?

It has been observed in many clinical trials and studies that tumors that have a high burden of mutations (TMB-High) have shown to respond much better to immunotherapy treatments. Therefore knowing the TMB score (tumor mutational burden) in your biopsy sample can help your medical team plan the most effective treatment plan.

Note – it has not yet been clearly established that TMB-High in itself as an indicator of patient success with immunotherapy response. This is now the focus of much reserach.

Levels of TMB

• Low TMB less than ≤5 mutations/Mb,
• Intermediate TMB is greater than >5 and less than <20,
• High TMB greater than ≥20 and less than <50, and
• Very high TMB greater than ≥50)” [Origin]

More detailed

• The TMB is defined as the total number of nonsynonymous mutations per coding area of a tumor genome. [Origin]
• TMB of a tumor sample is calculated by the number of non-synonymous somatic mutations (single nucleotide variants and small insertions/deletions) per mega-base in coding regions. 21 TMB represents both the stability level of the tumor genome and the heterogeneity of the tumor micro-environment. [Origin]
• TMB was studied both as a tiered variable (low ≤5 mutations/Mb, intermediate >5 and <20, high ≥20 and <50, and very high ≥50)” [Origin]

Discusses the relationship of High TMB and Checkpoint Biomarkers in relation to immunotherapies