• Background: Serrated polyposis syndrome is the most common colorectal polyposis syndrome. Its pathogenesis is still unknown and its diagnosis is based on clinical criteria. Despite advances in its knowledge, the intestinal microbiota of these patients has not been characterized, nor has the role of Fusobacterium nucleatum in their lesions been evaluated.
• Aim: The main objective is to compare the composition of the intestinal and oral microbiota of individuals diagnosed with serrated polyposis syndrome with individuals with sporadic serrated polyps, adenomatous polyps and without polyps. Among the secondary objective is to establish the prevalence of Fusobacterium nucleatum in oral and fecal samples.
• Methodology: Observational, case-control and multicenter study. Prospective inclusion for 24 months of all patients diagnosed with serrated polyposis syndrome, associated with three control groups: individuals without polyps, individuals with sporadic serrated lesions and individuals with adenomas. Clinical, histological, and endoscopic data will be recorded, and biological samples from saliva, and feces will be collected.

Inclusion Criteria:

- Individuals who meet the diagnostic criteria for serrated polyposis syndrome and who have a recent colonoscopy (<3 months) in which at least one serrated lesion is resected (defined as hyperplastic polyp or sessile serrated lesion / polyp) proximal to the rectum ≥ 5 mm.

2) Individuals who have a recent colonoscopy (<3 months) in which it is at least dry a serrated lesion proximal to the rectum ≥ 5 mm. Must not present ≥ 5 serrated lesions metachronous or synchronous. 3) Individuals who have had a recent colonoscopy (<3 months) with resection of the less one adenoma ≥ 5 mm. 4) Individuals who have had a recent colonoscopy (<3 months) without polyps.

Exclusion Criteria:

• Suspicion of hereditary syndromes of predisposition to CRC (> 20 metachronous adenomas, Familial adenomatous polyposis, Lynch syndrome, Peutz-Jeghers syndrome, Cowden, juvenile polyposis).
• Consumption of antibiotics, probiotics or prebiotics in the last 3 months.
• Incomplete colonoscopy or with inadequate preparation in some section.
• Adenomatous, serrated or indeterminate polyps synchronous in the inclusion colonoscopy except in the group of serrated polyposis syndrome.
• Colorectal cancer or hamartomatous polyps in inclusion colonoscopy.

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