Purpose An underlying factor for the failure of several clinical trials of anti-epidermal growth factor receptor (EGFR) therapies is the lack of an effective method to identify patients who overexpress EGFR protein. The quantitative dot blot method (QDB) was used to measure EGFR protein levels objectively, absolutely, and quantitatively. Its feasibility was evaluated for the prognosis of overall survival (OS) of patients with gastric cancer. Materials and Methods Slices of 2×5 μm from formalin-fixed paraffin-embedded gastric cancer specimens were used to extract total tissue lysates for QDB measurement. Absolutely quantitated EGFR protein levels were used for the Kaplan-Meier OS analysis. Results EGFR protein levels ranged from 0 to 772.6 pmol/g (n=246) for all gastric cancer patients. A poor correlation was observed between quantitated EGFR levels and immunohistochemistry scores with ρ=0.024 and P=0.717 in Spearman's correlation analysis. EGFR was identified as an independent negative prognostic biomarker for gastric cancer patients only through absolute quantitation, with a hazard ratio of 1.92 (95% confidence interval, 1.05–3.53; P=0.034) in multivariate Cox regression OS analysis. A cutoff of 208 pmol/g was proposed to stratify patients with a 3-year survival probability of 44% for patients with EGFR levels above the cutoff versus 68% for those below the cutoff based on Kaplan-Meier OS analysis (log rank test, P=0.002). Conclusions A QDB-based assay was developed for gastric cancer specimens to measure EGFR protein levels absolutely, quantitatively, and objectively. This assay should facilitate clinical trials aimed at evaluation of anti-EGFR therapies retrospectively and prospectively for gastric cancer.

Background: One causing factor underlying failures of several clinical trials of anti-EGFR therapies is the lack of effective method to select patients overexpressing EGFR protein. Quantitative Dot Blot method (QDB) is proposed here to measure EGFR protein levels objectively and quantitatively. Its feasibility was evaluated for prognosis of overall survival (OS) of gastric cancer patients. Methods: FFPE slices of 2X5 microM from gastric and Lung cancer specimens were used to extract total tissue lysates for QDB measurement. Absolutely quantitated EGFR protein levels were used for Kaplan-Meier Overall Survival (OS) analysis of gastric cancer patients. Results: EGFR protein levels ranged from 0 to 772 pmole/g for gastric cancer specimens (n=246), and from 0 to 2695 pmole/g for lung cancer patients (n=81). Poor correlation was observed between quantitated EGFR levels and IHC scores with r=0.018, p=0.786 from Spearman correlation analysis. EGFR was identified as an independent negative prognostic biomarker for gastric patients only through absolute quantitation, with HR at 2.29 (95%CI:1.23-4.26, p=0.0089) from multivariate cox regression OS analysis. A cutoff of 207.7 pmole/g was proposed to stratify gastric cancer patients, with 5-year survival probability at 37% for those whose EGFR levels were above the cutoff, and at 64% those below the cutoff based on Kaplan-Meier OS analysis. p=0.0057 from Log Rank test. Conclusion: A QDB-based assay was developed for both gastric and Lung cancer specimens to measure EGFR protein levels absolutely, quantitatively and objectively. This assay should facilitate clinical trials aiming to evaluate anti-EGFR therapies retrospectively and prospectively.