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.