Arginine methylation of EGFR: a new biomarker for predicting resistance to anti-EGFR treatment.

Arginine methylation of the epidermal growth factor receptor (meEGFR) increases the binding affinity of EGFR ligands and is reported to have a role in predicting response to anti-EGFR agents. This study investigated the predictive impact of meEGFR in metastatic colorectal cancer (mCRC) patients treated with anti-EGFR agents. Two patient cohorts were evaluated. Cohort 1 consisted of mCRC patients with documented disease progression following anti-EGFR treatment. Circulating tumor cells (CTCs) were isolated and distinguished based on CD45- and Epcam+ . Cohort 2 consisted of formalin fixed paraffin-embedded (FFPE) blocks from a prospective cohort. meEGFR in both cohorts was identified by positive staining for me-R198/200 EGFR signal. CTCs were identified in 30 out of 47 cases in cohort 1. Of those 30, meEGFR-CTCs were identified in 19 cases. Mean total meEGFR-CTCs counts was 2.3 (range 0-30) cells per 7.5 ml. There was no association between meEGFR-CTCs and clinic-pathological-molecular features. In RAS wt / BRAF wt patients with high levels of meEGFR-CTCs ratio (≥ 0.23) had significantly inferior PFS with anti-EGFR treatment (HR = 3.4, 95% CI 1.5-7.9, P = 0.004). By contrast, high levels of meEGFR in the untreated tumor tissues had no correlation with anti-EGFR treatment duration in cohort 2. Therefore, meEGFR-CTCs may have the potential to serve as a "liquid biopsy" biomarker to predict anti-EGFR treatment efficacy.