Familial adenomatous polyposis (FAP) is an autosomal dominant inherited disorder linked to a mutation in the APC gene, associated with the development of multiple colonic and duodenal adenomas, which in 100% of cases progress to colorectal cancer (CRC) if left untreated. Management of affected patients is usually based on prophylactic total colectomy with or without rectal preservation, followed by regular endoscopic surveillance of the duodenum and rectum or ileal reservoir. However, there is considerable inter- and intra-familial variability in the rate of adenoma appearance and development for identical mutations. This strongly suggests the additional role of environmental factors. Recently, the gut microbiota has been identified as a co-factor of carcinogenesis in patients with FAP, but no prospective evaluation of the association between the incidence and severity of adenomatous proliferations and a microbiological signature has been studied, particularly at duodenal level in operated patient.

Inclusion Criteria:

• ≥18 years
• Non-opposition obtained
• Prophylactic colectomy for at least 2 years in the context of APC-related familial adenomatous polyposis with ileorectal or ileoanal anastomosis
• Included in the national POLYPOSE database
• Regular endoscopic follow-up with upper and lower GI endoscopy at Hôpital Edouard Herriot or Hôpital de la Croix-Rousse
• Having performed at least 2 endoscopies as part of follow-up

Exclusion Criteria:

• Antibiotic therapy within 2 months prior to stool sampling
• Taking probiotics for less than 1 month
• Person deprived of liberty by judicial or administrative decision

Patients with proven familial adenomatous polyposis genetically operated (total colectomy with ileoanal or ileorectal anastomosis), included in the national POLYPOSE database and with regular endoscopic follow-up with upper and lower GI endoscopy at Hôpital Edouard Herriot, Lyon, France or Hôpital de la Croix-Rousse, Lyon, France