Identification of taxonomic changes in feces bacteriome associated with colorectal polyps and cancer: potential biomarkers for early diagnosis

Colorectal cancer (CRC) is a disease of worldwide concern, which has an increasingly established relationship with the intestinal microbiota. Most of the cases of sporadic CRC emerge in patients with polyps, which also are influenced by gut microbiota. In this study, we utilized shotgun metagenomics to analyze the taxonomic diversity of Bacteria present in fecal samples of control, polyps, and CRC patients. The samples were collected between 2017 and 2018 by the Biodonostia Health Research Institute - Donostia Hospital in the city of San Sebastian, Spain, following the 2003 European Guidelines and the 2006 National Strategy against Cancer. The population-based screening of CRC was approved by the Basque Autonomous Government and implemented in 2009. The screening is based on the detection of occult blood in feces (FOB) using a biennial quantitative fecal immunochemical test (FIT), targeting women and men between 50 and 69 years old and a colonoscopy under sedation for FIT positive cases. 90 samples were collected and further divided into three groups based on colonoscopy results: control group (n31-60; stool samples from individuals with colonoscopy showing no intestinal lesions, no history of diarrhea, and no history of previous intestinal infection), polyps group (n1-30; stool samples from individuals with colonoscopy showing polyps on the surface of the colon or rectum), and the CRC group, which consists of individuals with biopsies confirming malignancy of colon or rectum lesions (n61-90).