Counting mutations as an ICI biomarker–useful but limited compared to functional measurement.
The rationale for TMB as an immunotherapy biomarker is logical: more mutations ' more neoantigens ' more T cell targets ' better ICILoading... response. This explains why highly mutated cancers (melanomaLoading..., lung) respond well to checkpoint blockade.
TMB-high status (10 mutations/Mb) was approved as a tissue-agnostic biomarker for pembrolizumab, meaning any solid tumor meeting this threshold is potentially eligible for treatment.
What It Measures: Tumor mutational burden counts how many mutations a tumor has (mutations per megabase of DNA).
Why It Matters: More mutations = more abnormal proteins (neoantigens) = more targets for immune recognition. High-TMB tumors tend to respond better to checkpoint inhibitors.
TMB has significant limitations as a predictive biomarker. It doesn't measure whether checkpoint pathways are actually engaged. A tumor may have high TMB but evade immunity through mechanisms other than PD-1/PD-L1Loading.... Conversely, some TMB-low tumors respond well to immunotherapy.
TMB also requires next-generation sequencing, adding cost and turnaround timeLoading.... Different assays use different gene panels and thresholds, creating standardization challenges.
Not Perfect: High TMB doesn't guarantee response. Some high-TMB patients don't respond; some low-TMB patients do.
What's Missing: TMB tells you about mutation load but not about actual immune engagement. A highly mutated tumor with suppressed immunity might not respond.
TMB and functional biomarkersLoading... address different questions:
TMB asks: Does this tumor have many mutations that might generate neoantigens?
iFRET asks: Are checkpoint receptors and ligands actually interacting to suppress immunity?
These are complementary. A tumor could be TMB-high but have low checkpoint engagement (immune escape via other mechanisms), or TMB-low but highly checkpoint-dependent. Functional measurement provides the direct answer.
Complementary Information:
• TMB tells you: Many potential targets exist
• Checkpoint engagement tells you: Immune suppression is active
Best Candidates: High TMB + high checkpoint engagement = lots of targets AND active suppression to relieve. Potentially ideal for checkpoint blockade.
