Colorectal cancer (CRC) has been associated with changes in volatile metabolic profiles in several human biological matrices. This enables its non-invasive detection, but the origin of these volatile organic compounds (VOCs) and their relation to the gut microbiome are not yet fully understood. This systematic review provides an overview of the current understanding of this topic. A systematic search using PubMed, Embase, Medline, Cochrane Library, and the Web of Science according to PRISMA guidelines resulted in seventy-one included studies. In addition, a systematic search was conducted that identified five systematic reviews from which CRC-associated gut microbiota data were extracted. The included studies analyzed VOCs in feces, urine, breath, blood, tissue, and saliva. Eight studies performed microbiota analysis in addition to VOC analysis. The most frequently reported dysregulations over all matrices included short-chain fatty acids, amino acids, proteolytic fermentation products, and products related to the tricarboxylic acid cycle and Warburg metabolism. Many of these dysregulations could be related to the shifts in CRC-associated microbiota, and thus the gut microbiota presumably contributes to the metabolic fingerprint of VOC in CRC. Future research involving VOCs analysis should include simultaneous gut microbiota analysis.

INTRODUCTION: Early detection of colorectal cancer (CRC) by screening programs is crucial because survival rates worsen at advanced stages. However, the currently used screening method, the fecal immunochemical test (FIT), suffers from a high number of false-positives and is insensitive for detecting advanced adenomas (AAs), resulting in false-negatives for these premalignant lesions. Therefore, more accurate, noninvasive screening tools are needed. In this study, the utility of analyzing volatile organic compounds (VOCs) in exhaled breath in a FIT-positive population to detect the presence of colorectal neoplasia was studied. METHODS: In this multicenter prospective study, breath samples were collected from 382 FIT-positive patients with subsequent colonoscopy participating in the national Dutch bowel screening program (n = 84 negative controls, n = 130 non-AAs, n = 138 AAs, and n = 30 CRCs). Precolonoscopy exhaled VOCs were analyzed using thermal desorption-gas chromatography-mass spectrometry, and the data were preprocessed and analyzed using machine learning techniques. RESULTS: Using 10 discriminatory VOCs, AAs could be distinguished from negative controls with a sensitivity and specificity of 79% and 70%, respectively. Based on this biomarker profile, CRC and AA combined could be discriminated from controls with a sensitivity and specificity of 77% and 70%, respectively, and CRC alone could be discriminated from controls with a sensitivity and specificity of 80% and 70%, respectively. Moreover, the feasibility to discriminate non-AAs from controls and AAs was shown. DISCUSSION: VOCs in exhaled breath can detect the presence of AAs and CRC in a CRC screening population and may improve CRC screening in the future.

Introduction Early detection of colorectal cancer (CRC) and clinically relevant (advanced) adenomas leads to a significant reduction of CRC-related mortality and morbidity. However, the faecal immunochemical test (FIT) suffers from a high number of false-positive results and is insensitive to detecting advanced adenomas, resulting in false-negative results for these premalignant lesions. Therefore, more accurate, non-invasive screening tools are needed for the detection and prognostication of colorectal neoplasia. Previous research on volatile organic compounds (VOCs) analysis in breath and faeces has shown to be promising potential biomarkers for this purpose. Several VOC-sampling methods, including breath sampling, have improved significantly over the recent years resulting in an increased reliability of measurements. Therefore, we aim to identify relevant VOC profiles in exhaled breath and faeces for the diagnosis of colorectal neoplasia while taking into account relevant confounding factors. Follow-up data will be used to identify relevant VOC profiles in exhaled breath and faeces for the prognostication of colorectal neoplasia. Finally, a biobank will be set up for future research questions on this topic. Methods and analysis Subjects with positive FIT within the Dutch national CRC cancer screening programme are included. Subjects are asked to fill in questionnaires and exhaled breath, faeces and blood are sampled prior to colonoscopy. All subjects are asked to fill in follow-up questionnaires at years 1 and 5 of the study. In case of surveillance colonoscopies, subjects are asked to provide exhaled breath, faeces and blood prior to the colonoscopy again. Breath sampling is performed using the ReCIVA breath sampler. VOCs in breath and faeces are analysed using gas-chromatography-mass spectrometry (GC-MS). Raw GC-MS data is preprocessed and analysed using machine learning techniques. Ethics and dissemination The study is approved by the medical ethics committee at the Maastricht University Medical Center (NL74844.068.20) in November 2021 and started inclusion in January 2022.