TMB-High (Tumor Mutational Burden) Tumors ? Candidates For Immunotherapy

TMB-High (Tumor Mutational Burden) tumors represent a distinct group of cancers characterized by a high number of somatic mutations within the tumor genome, typically defined as 10 or more mutations per megabase (mut/Mb). This elevated mutational load leads to the generation of numerous neoantigens, which can be recognized by the immune system’s T-cells as foreign, thereby increasing tumor immunogenicity.

These tumors are considered prime candidates for immunotherapy, particularly immune checkpoint inhibitors (ICIs) such as pembrolizumab, which have been FDA-approved for solid tumors exhibiting TMB-H status regardless of the tumor origin. The rationale is that a higher number of neoantigens increase the likelihood of effective T-cell recognition and tumor eradication when immune checkpoints like PD-1 or CTLA-4 are blocked. Clinical studies have demonstrated that patients with TMB-H tumors often show significantly better objective response rates, durable clinical benefits, progression-free survival, and overall survival after immunotherapy compared to those with low TMB.

However, TMB is an imperfect biomarker; not all TMB-H patients respond to ICIs, and some with low TMB do benefit, highlighting the complexity of tumor-immune interactions. Factors such as MHC presentation, T-cell receptor diversity, and tumor microenvironment also influence immunotherapy outcomes. Despite these limitations, TMB-H continues to be a valuable predictive biomarker guiding treatment decisions in precision oncology, helping clinicians identify patients most likely to benefit from immunotherapy.