Review: Predictive and prognostic markers for epidermal growth factor receptor inhibitor therapy in non-small cell lung cancer

Epidermal growth factor receptor (EGFR) related therapies - mainly tyrosine kinase inhibitors (TKIs) such as erlotinib and gefitinib, but also monoclonal antibodies targeting EGFR, for example, cetuximab - have been investigated in numerous settings in non-small cell lung cancer (NSCLC) and in different combinations. The overall clinical benefit of EGFR TKI therapy is roughly 10-30%, with higher benefit in nonsmoker Asiatic women with EGFR-mutated adenocarcinoma. Currently, there are several biomarkers that are able to direct and predict the yield of EGFR-related therapies in NSCLC. These include EGFR mutation status, EGFR protein expression, EGFR gene copy number and a serum proteomic marker (Veristrat^®, Biodesix; CO). The usage of such biomarkers is important from many aspects. First, it helps clinicians to make the right treatment decisions and second, it leads to a wiser usage of financial resources. This review will focus on EGFR-related biomarkers for their prognostic power and their ability to predict clinical benefit from EGFR-related therapy.