Mutation detection and semi-quantification using two plasma EGFR mutation assay kits with 47 serially diluted contrived samples. The numbers in the green-, yellow-, and blue-tinged boxes indicate the SQIs of the mutation-detected samples and the color tone indicates the SQI rank (light tones indicate lower SQIs and dark tones indicate higher SQIs). The en dash (–) in each white-colored box (except for the en dash indicating EGFR-mutant genotype) indicates that at least one of the EGFR mutations was detected in the corresponding sample using the corresponding plasma assay kits. NM (no mutation detected by cobasv2 analysis) or W (wild type by Mutyper analysis) written in blue in each white box indicates that no EGFR mutations were detected in the corresponding samples. The red-bordered boxes indicate the predicted limit of detection values of the two kits for the three major EGFR-mutant genotypes. The same upper-case or lower-case superscript letter in each dilution series box indicates the same batch analysis. The asterisk in each box indicates that the same mutant was observed following replicate analysis using the remaining aliquots of the extracted DNA samples. The correlation coefficients (ρ) between the dilution effect and SQI rank and P written in black were obtained using Spearman's rank correlation analysis. P or not significant (NS; P>0.05) written in white was obtained using Steiger's Z-test (St-Z), which served to calculate the difference between the two correlation coefficients (cobasv2-ρ vs Mutyper-ρ).

Abbreviations: EGFR, epidermal growth factor receptor; E19del, an in-frame deletion in exon 19; L858R, p.Leu858Arg mutation; T790M, p.Thr790Met mutation; cobasv2, cobas EGFR Mutation test v2; Mutyper, PANAMutyper-R-EGFR; SQI, semi-quantitative index; St-Z, Steiger's Z-test; NS, not significant.