EGFR mutation testing on cell free circulating tumour DNA: the Birmingham Molecular Pathology Diagnostic Service


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Claire Swift1,Matthew Smith1,Amina Mulla1,Frances Hughes1,Brendan O'Sullivan1,Gary Middleton1,Philippe Taniere1
1Queen Elizabeth Hospital Birmingham

Abstract

Background

Activating mutations in the EGFR gene are detected in ~10% of NSCLC; these patients demonstrate a high response rate and prolonged progression-free survival when treated with anti-EGFR TKI therapies. The emergence of the resistance mutation p.T790M occurs in ~50% of EGFR-mutant NSCLC that develop progressive disease following treatment.

QEHB MPDS performs >300 EGFR FFPET tests a month. Inadequate tumour sampling or poor performance status renders some patients unsuitable for testing. It’s been well established that ctDNA provides a viable blood-based marker for molecular testing, with ctDNA providing an alternative approach to testing in these patients.

QEHB MPDS is one of the first NHS diagnostic laboratories to offer a ctDNA service for the detection of EGFR mutations.

Method

QEHB MPDS supplies users with PAXgene tubes. ctDNA is extracted using the cobas® cfDNA Sample Preparation Kit (Roche). EGFR status is determined using the cobas® EGFR Mutation Test Kit (Roche), a real-time PCR assay which detects 42 EGFR mutations.

Results

During service verification, the analytical test sensitivity and specificity was 89%/100% in patients that had yet to commence treatment, and 62%/100% in patients under TKI therapy, respectively. In both clinical situations the sensitivity was shown to increase with the clinical stage of the tumour.

To date QEHB MPDS has clinically tested 68 patient samples.

Conclusion

EGFR testing in ctDNA has been successfully introduced into the clinical service at QEHB for the diagnosis and monitoring of patients. The sensitivity of the ctDNA assay is lower than that observed in FFPET; it is important to realise that a ‘mutation not detected’ result does not exclude the presence of an EGFR mutation and reflex tissue testing should be considered. Conversely, a positive result guarantees a positive result. EGFR testing in plasma is an ‘add-on’ service for detecting mutations in clinical practice and cannot fully replace EGFR testing in tissue.