Quantification of epidermal growth factor receptor (EGFR) mutation may be a predictor of EGFR‐tyrosine kinase inhibitor treatment response

BACKGROUND: Epidermal growth factor receptor (EGFR) gene mutation is a reliable predictive factor for response to EGFR‐tyrosine kinase inhibitors (TKIs). The quantified EGFR value may also predict response and survival within an EGFR mutated group. METHODS: We conducted a retrospective study of 836 lung cancer patients. The patient sample was divided into two groups based on the mean delta cycle threshold (∆Ct) value. EGFR mutation tests using peptide nucleic acid (PNA)‐mediated clamping polymerase chain reaction (PCR) were performed. The efficiency of PCR clamping was determined by measuring the Ct value and EGFR quantification was determined by the corrected ∆Ct value. RESULTS: EGFR mutation positivity was 30.1% and there were 235 single activating mutations. In this mutation group, the higher corrected ∆Ct value (≥ mean value) group showed better objective response (70.9% vs. 54.9%, P = 0.022) and clinical benefit rates (86.4% vs. 68.3%, P = 0.003) than the lower group. In addition, corrected ∆Ct values were significantly and inversely correlated with disease response (r = −0.184, P = 0.017). In multivariate analysis, both female gender (P = 0.014) and higher corrected ΔCt value (P = 0.012) were independent predictive factors for better clinical benefit rate. The higher corrected ΔCt value group had a tendency for longer progression‐free survival than the lower group (P = 0.050). CONCLUSION: The corrected ∆Ct value, which refers to EGFR quantification by PNA‐mediated PCR clamping, can predict better clinical response to EGFR‐TKI therapy. However, further study is warranted to determine its value as a biomarker to reflect survival.