Determination of Microbiological Factors Associated With Poor Response to Neoadjuvant Treatment in Rectal Cancers

Inclusion Criteria: 1. Histologically proven lower and mid-rectal adenocarcinoma at clinical stage II and III 2. Patient is to receive neoadjuvant treatment (radiochemotherapy or chemotherapy or radiotherapy). Induction chemotherapy such as folfox or folfirinox is allowed 3. Patient who has signed the informed consent of the study 4. Male or female ≥ 18 years old 5. Appropriate contraceptive measures should be used by both men and non-menopausal women before entering the trial until at least 8 weeks after the last course of radiochemotherapy. The investigator should inform the patient about the contraceptive measures to be used. Exclusion Criteria: 1. Antibiotic treatment at the time or in the month preceding stool sampling 2. Presence of an ostomy 3. Previous treatment for rectal cancer 4. Patient not affiliated to a French social protection system 5. Patient not in favour of good compliance with treatment for psychological, family, social or geographical reasons 6. Legal incapacity (Patient under curatorship or guardianship) 7. Prior radiation therapy or pelvic curia in the year prior to inclusion 8. History of other cancers in the last 5 years (except for in-situ cervical carcinomas and non-melanoma skin carcinomas treated optimally) 9. Pregnant or breastfeeding woman