Tumor mutational burden (TMB)
The number of mutations in a tumor's genome — a rough proxy for how many neoantigen targets it might offer.
TMB counts the mutations carried by a tumor. More mutations generally mean more potential neoantigens, which is why high-TMB cancers (like melanoma and some lung cancers) have been early focuses for neoantigen vaccines and immunotherapy.
TMB is only a starting point, though — most mutations never become presented, immunogenic neoantigens, so a high count doesn't guarantee good targets. It's a screening signal, not a selection method.
Is high tumor mutational burden good?
For immunotherapy, generally yes — a higher mutation count means more potential neoantigens for the immune system to target, and high-TMB cancers (e.g. melanoma, some lung cancers) tend to respond better to checkpoint inhibitors. But TMB is a rough screening signal, not a guarantee, since most mutations never become presented, immunogenic neoantigens.
What is the difference between TMB and neoantigen burden (TNB)?
TMB counts all mutations in a tumor's genome. Neoantigen burden (TNB) counts only the subset of mutations predicted to produce neoantigens that are actually presented on HLA. TNB is a more refined, biology-aware signal, but it depends on prediction quality; TMB is simpler to measure and more widely used clinically.