A comparative study of EGFR oncogenic mutations in matching tissue and plasma samples from patients with advanced...

Plasma based EGFR mutation analysis is emerging as a viable alternative to tumour tissue genotyping for patients with non-small cell lung carcinoma (NSCLC). The purpose of the study was to determine the degree of concordance between EGFR genotypes derived from matching tissue and blood samples.

EGFR activating mutations L858R, exon 19 deletions, G719A/C/S and L861Q as well as resistance mutations T790M and exon 20 insertions were co-analysed in 61 matching tissue and blood biopsies collected from NCSLC patients. Tissue and plasma genotyping was performed by amplification refractory mutation system PCR (ARMS-PCR) and circulating single molecule amplification and re-sequencing technology (cSMART), respectively.

Of the 61 paired samples, 44 (72.1%) were fully concordant, 2 (3.3%) were partially concordant and 15 (24.6%) were discordant for EGFR genotypes. The discordance was bidirectional with tissue and plasma failing to reveal the equivalent mutation in eight and nine cases, respectively. Benchmarking against ARMS-PCR tissue biopsy results as the gold standard, the sensitivity and concordance rates for plasma mutation detection by cSMART assay were 72.7% and 90.2% (L858R), 72.7% and 86.9% (exon 19 deletions) and 100% and 98.4% (T790M).

The cSMART assay was highly reliable and accurate for plasma EGFR genotyping. Based on discordance trends, tumour heterogeneity was suspected to be the major factor preventing a concordant diagnosis in matching samples.