Urinary EGFR as a marker of urinary bladder cancer.

Abstract

327 Background: Better biomarkers must be found to develop clinically useful urine tests for urothelial bladder cancer (UBC). Our objective was to identify proteins released by bladder cancer cells in vitro and assess their potential as urinary biomarkers. EGFR was identified as a promising biomarker and is overexpressed in numerous cancers including UBC. EGFR is a member of the ErbB family of transmembrane tyrosine kinase receptors. It is a 170kDa protein that facilitates cell growth and differentiation by acting upon downstream signaling pathways. Methods: We used shotgun proteomics to identify the proteins released into culture media by 8 UBC cell lines. These data were compared with protein expression data from the Human Protein Atlas. EGFR was measured by ELISA in the urine of 436 patients with primary bladder cancer (prior to commencing treatment) and 60 non-UBC control subjects (all samples were obtained from the Bladder Cancer Prognosis Programme). Outcomes were, presence of bladder cancer (yes/no) and bladder cancer-specific survival. Data were analysed with Mann-Whitney tests and Cox multivariable modelling. Results: EGFR was selected as a candidate biomarker because it was released by 5 out of 8 bladder cancer cell lines, but not by a ‘normal urothelium’ cell line, and is documented as highly overexpressed in UBC in the Human Protein Atlas. A soluble form of EGFR is detectable in urine and is increased in some patients with high-grade bladder cancer. With a cut-off defined as mean + 2 SD (630pg EGFR/mg creatinine), elevated urinary EGFR was an independent indicator of poor bladder cancer-specific survival with a hazard ratio of 2.89 (95% CI 1.81-4.62, p<0.001). In multivariable models urinary EGFR and EpCAM (previously reported) are strong independent predictors of bladder cancer-specific survival. Urinary EGFR is not useful as a diagnostic marker. Conclusions: Aggressive bladder cancers shed the ectodomain of EGFR into urine. Measuring urinary EGFR and EpCAM may represent a simple and useful approach for fast-tracking the investigation and treatment of those patients with the most aggressive bladder cancers, expediting their care to improve outcomes.