Clinical implementation of plasma EGFR T790M testing using droplet digital PCR in TKI-resistant NSCLC patients
Dana Leng Hui Chan1, Grace Li Xian Toh1, Liuh Ling Goh1
1Molecular Diagnostic Laboratory, Tan Tock Seng Hospital, Singapore.
Background:
Majority of non-small cell lung cancer (NSCLC) patients progressed on epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) due to acquired T790M mutation. Blood sample is increasingly used in clinical setting for EGFR T790M detection and our laboratory employed the droplet digital PCR (ddPCR) methodology for testing. This study investigated the positive rate, specimen type for rebiopsy and clinical impact of blood-based EGFR T790M testing.
Methods:
We retrospectively evaluated clinical samples that underwent plasma EGFR T790M testing in TTSH Molecular Diagnostic Laboratory from August 2017 to September 2019. Data on diagnosis, EGFR activating and T790M mutations, and treatment strategies were recorded.
Results:
A total of 104 progressive NSCLC cases were included in this study. Overall, 46 patients (44.2%) were tested T790M positive, and 47.8% of these tested positive had low levels (defined as ≤3% fractional abundance and <50 copies/mL plasma), which may be missed by the conventional methods with lower sensitivity. Of these tested with low T790M abundance, 77.3% subsequently received osimertinib. Activating mutations were not detected in 42 (40.4%) cases, indicating that the tumors were not actively shedding ctDNA. Among these, 24 patients underwent repeat testing with tissue or blood specimens. Thirteen patients were subsequently tested T790M positive and 12 of them switched treatment to osimertinib. The recommendation to repeat testing with a different biopsy or after a suitable interval increased the overall positive rate to 56.7% (59/104).
Conclusion:
The use of a highly sensitive platform such as ddPCR for the detection of low abundance T790M, and the approach of repeat testing in cases with insufficient ctDNA increased the positive rate. This in turn identified more patients who are eligible for targeted therapy.
Insights
Liquid biopsy using droplet digital PCR (ddPCR) improves detection of T790M mutations in non-small cell lung cancer (NSCLC) patients. Repeat testing increases positive rates, identifying more patients for targeted therapy.
Area of Science:
- Oncology
- Molecular Diagnostics
- Genetics
Background:
- Non-small cell lung cancer (NSCLC) frequently develops resistance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) due to the acquired T790M mutation.
- Blood-based testing for EGFR T790M mutations is gaining clinical utility.
- Droplet digital PCR (ddPCR) is a sensitive method for detecting T790M in plasma.
Purpose of the Study:
- To investigate the positive rate of blood-based EGFR T790M testing using ddPCR.
- To evaluate the impact of specimen type for rebiopsy on detection rates.
- To assess the clinical utility of T790M testing in guiding treatment decisions for NSCLC patients.
Main Methods:
- Retrospective evaluation of 104 progressive NSCLC cases undergoing plasma EGFR T790M testing.
- Analysis of diagnostic data, EGFR mutations (activating and T790M), and treatment strategies.
- Comparison of ddPCR sensitivity with conventional methods and assessment of repeat testing outcomes.
Main Results:
- An overall T790M positive rate of 44.2% was observed, with 47.8% of positive cases showing low abundance mutations.
- Repeat testing in cases with initially undetectable ctDNA increased the overall positive rate to 56.7%.
- Patients with low abundance T790M or those identified through repeat testing were often eligible for targeted therapy with osimertinib.
Conclusions:
- Highly sensitive ddPCR platforms enhance the detection of low-abundance T790M mutations in plasma.
- A strategy of repeat testing in cases with insufficient ctDNA significantly improves the positive detection rate.
- Improved T790M detection rates enable more NSCLC patients to receive appropriate targeted therapy.
