🧬 FAST FACTS: TUMOUR MUTATIONAL BURDEN TESTING
👩⚕️ Dr Nicole Rossum
🔍 Understanding Tumour Mutational Burden (TMB) Testing
Tumour Mutational Burden (TMB) is a measure of the total number of somatic mutations found in the DNA of cancer cells.
📏 It’s expressed as mutations per megabase (mut/Mb) of DNA sequenced.
🧪 It reflects how many genetic changes have occurred in the tumour’s genome.
💡 Why Test for TMB?
Tumours with higher mutational loads:
- 🧫 Are more likely to generate neoantigens
- ⚔️ Increase immunogenicity
- 💉 Improve likelihood of response to immunotherapy, especially immune checkpoint inhibitors (anti–PD-1/PD-L1 therapies)
📊 A high TMB is commonly defined as ≥10 mut/Mb, though some tumour types may benefit at higher thresholds.
🧠 Clinical Relevance
TMB testing is recommended for:
- 🧍♂️ Advanced, unresectable, or metastatic solid tumours
- 🧪 Cases with no satisfactory alternative treatment options
- 🎯 Identifying candidates for immune checkpoint inhibitor therapy
📚 KEYNOTE-158 Trial:
- Studied pembrolizumab in previously treated, advanced solid tumours
- 🧬 Patients with TMB-high (≥10 mut/Mb) had a 29% response rate vs. 6% in non-TMB-high
- ✅ Led to regulatory approval for pembrolizumab in TMB-high tumours, regardless of histology
🧪 NGS-Based TMB Testing Now Available at Ampath
🔬 Ampath offers Next Generation Sequencing (NGS) based TMB testing
🧾 Can be requested:
- Individually
- As part of the Oncomine™ Comprehensive Assay Plus
🧾 TMB NGS Testing Panel Overview
🧬 Test Mnemonic: TMB🩺
Clinical Indication: Identify oncology patients for immune checkpoint inhibitor therapy🧫
Specimen Type: FFPE tissue: 8–12 normal slides (not charged), 10 micron thick unstained recuts in Eppendorf tube or paraffin block
Turnaround Time: 14 working days
📧 Contact for more info: ngs@ampath.co.za
🌐 ampath.co.za