Home › Biomarkers › TMB (tumor mutational burden)

TMB (tumor mutational burden) testing: what it means for you

Waiting on test results can feel like one more hard thing, for you and the people who love you. Here's what the TMB (tumor mutational burden) test looks for and how it can help your care team pick the treatment most likely to work for you.

ℹ️ General information to help you and your loved ones talk with your care team, not medical advice. Read our disclaimer.

Matters most in: Lung cancer, Colorectal cancer, Breast cancer, Ovarian cancer, Prostate cancer

Why it matters

Tumors with many mutations (TMB-high, at least 10 per megabase on an FDA-approved test) may be easier for the immune system to spot. Keytruda is approved for TMB-high solid tumors that have grown after treatment when there are no better options.

Treatments it can point to

• Immunotherapy such as Keytruda (Keytruda (pembrolizumab))

Only your care team can say which treatment fits you. Drug approvals depend on cancer type, stage and prior treatment.

Tissue vs. blood testing

Tissue from a large gene panel; some blood panels also estimate it.

Most tests use a piece of tumor tissue from a biopsy or surgery. Some can also use a blood sample (a 'liquid biopsy') that looks for tumor DNA floating in the blood. Blood tests are easier and faster, but they can miss a change that a tissue test would find, so a negative blood test is often followed by a tissue test.

❓ Questions you and your loved ones can ask

• Was TMB part of my gene panel, and what was the number?
• When will my results be back, and will treatment wait for them?
• Will my insurance cover this test?

Written by the Cancer Side Effects Guide team from FDA labels and leading cancer centers. Not medical advice. · Last updated: October 15, 2026 · How we write