Abstract C11: Protein biomarkers predictive of outcome in EGFR inhibitor-treated non-small cell lung cancer patients with EGFR wildtype

Abstract

Abstract Background: EGFR inhibitors, erlotinib and gefitinib, cause tumor shrinkage in approximately 70% of non-small cell lung cancer (NSCLC) patients with activating mutations in EGFR, but may also be efficient in a subset of patients with EGFR wildtype, as indicated by a retrospective analysis of the BR.21 trial. However, there is currently a lack of biomarkers predictive for outcome of EGFR inhibitor-treated NSCLC patients with EGFR wildtype. The identification of such biomarkers was the aim of this study. Materials and methods: Formalin-fixed paraffin-embedded tissue blocks from 50 NSCLC patients with EGFR wildtype, who received treatment with erlotinib/gefitinib were included and stratified according to progression-free-survival (PFS). Twelve patients experienced no progression for >6 months (Good Response Group), while 38 patients experienced progression in <6 months (Poor Response Group). From formalin-fixed paraffin-embedded surgical resections, areas of high tumor content were isolated; peptides were extracted in triethyl ammonium bicarbonate/acetonitrile buffer by heat-induced antigen retrieval, and then fractionated by hydrophilic-interaction liquid chromatography (HILIC) followed by quantification and identification by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Samples were analyzed in technical duplicates, and only proteins identified with minimum 2 unique peptides were used for further analysis. Results: The patient cohort represented 20 men and 30 women. Two were non-smokers, 45 were smokers/former smokers and three were unknown. 42 exhibited adenocarcinoma histology and eight exhibited bronchioalveolar carcinoma histology. The majority of patients were treated with erlotinib (n = 47), while three received gefitinib. Mean PFS of patients in the Good Response Group was 455 days, while patients in the Poor Response Group had a mean PFS of 66 days, indicating that there are indeed patients with EGFR wildtype who benefit from EGFR inhibitors. From the quantitative LC-MS/MS analysis, we identified and quantified 3152 high-confident proteins across the 50 patients with ≥2 unique peptides. Softwares R and GProX were used for statistical analysis. Data was quantile normalized and revealed 30 proteins which were found to be differentially expressed between the two groups with a p-value <0.01. Among the most differentially expressed proteins, we found proteins involved with cytoskeletal rearrangement, intracellular transport, protein translation, transcription regulators and kinases. Conclusions: From the PFS analysis of our patient cohort, it is clear that patients exhibiting EGFR wildtype may also benefit from treatment with EGFR inhibitors. Using unbiased mass spectrometry, we identified 30 differentially expressed proteins with the potential to predict outcome of EGFR inhibitor-treated NSCLC patients with EGFR wildtype. Citation Format: Kirstine Jacobsen, Brian Hood, Karen Ege Olsen, Thomas Conrads, Henrik Ditzel. Protein biomarkers predictive of outcome in EGFR inhibitor-treated non-small cell lung cancer patients with EGFR wildtype. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C11.