Abstract 4523: Stool proteomics reveals new candidate biomarkers for colorectal cancer screening

Abstract

Abstract Background Colorectal Cancer (CRC) screening can save many lives. Many invitational large scale screening programs worldwide use stool tests like the fecal immunochemical tests (FIT), which detects human hemoglobin. Tumor-specific biomarkers have the potential to improve the performance of these tests but so far, no protein-based fecal test has proved better than the FIT. Although most biomarker discoveries are done in tumor-tissues, the presence and/or chemical nature of biomarkers may be different in samples that ultimately will be used for screening like stool. Measuring biomarkers directly in stool samples may therefore yield candidate CRC biomarkers that are stable in the fecal environment. Aim The aim of the present study was to identify tumor-specific protein based biomarkers for the early detection of CRC, by applying in-depth proteomics to stool samples from CRC patients and healthy controls. Material and method Stool samples were obtained from 10 subjects with negative colonoscopy and from 12 CRC patients. Proteins were analyzed by in-depth proteomics using gel electrophoresis and nano Liquid Chromatography coupled to tandem mass spectrometry (nano LC-MS/MS). Resulting MS/MS spectra were searched against the human IPI database (version 3.62). Proteins were analyzed by hierarchical cluster analysis and visualized in a heat map. Non-paired statistical analysis of spectral count data from human proteins was performed using a beta-binomial test. Verification of candidate biomarkers was performed by Selected Reaction Monitoring Mass Spectometry (SRM-MS). Results In total 830 human proteins were identified of which 221 were present at different levels in stool samples from CRC patients compared to control subjects. Of these, 134 proteins were significantly enriched in CRC. Unsupervised hierarchical cluster analysis revealed two clusters. One cluster contained nine CRC stool samples, the other cluster contained all ten control stool samples together with three CRC stool samples. SRM-MS analysis of selected candidate biomarkers on the same stool samples verified the results obtained by LC-MS/MS. Conclusion Proteome profiling on stool revealed 134 proteins significantly enriched in CRC compared to control stool samples, of which a sub set could be verified by SRM-MS. Validation in an independent series of stool samples collection (n=200) by SRM-MS is in process. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4523. doi:1538-7445.AM2012-4523