A Prospective Feasibility Study Evaluating Extracellular Vesicles Obtained by Liquid Biopsy for Neoadjuvant Treatment Response Assessment in Rectal Cancer

Inclusion Criteria: * Adenocarcinoma of rectum histologically proven * Location ≤ 10 cm from the anal margin * Stage T3T4, or T2 if low rectal cancer * With indication of radiochemotherapy alone or chemotherapy followed by chemoradiotherapy prior to total mesorectal surgery or transanal surgery * No metastasis * Operable patient * Patient ≥ 18 years old * Patient likely to receive radiation therapy and chemotherapy. * No history of pelvic radiotherapy for any reason * No history of chemotherapy unless it was more than 10 years ago * Effective contraception for patients of childbearing age: male and non-menopausal women must agree to use two medically validated methods of contraception (one for the patient and the other for the partner) during treatment and less up to 6 months for men and 4 months for women after last treatment * Patient information and obtaining free, informed and written consent, signed by the patient and his investigator. * Affiliate subject or beneficiary of a social security scheme of a member country of the European Community (article L1121-11 of the Code of Public Health) Exclusion Criteria: * Tumor of the upper rectum (\> 10 cm from the anal margin) * Metastatic disease . T1 stage tumor * History of pelvic radiotherapy and chemotherapy * Contraindication to chemotherapy and / or radiotherapy . Insufficient tumoral sample on initial rectal biopsy for performing molecular analysis of tumor by NGS. * Other concomitant cancer or history of cancer other than treated in situ cervix cancer or basal cell or squamous cell carcinoma * Pregnant woman, likely to be pregnant or breastfeeding * Symptomatic cardiac and / or coronary insufficiency * Severe renal impairment (creatinine clearance less than 30ml / min) * Full or partial deficiency in dihydropyrimidine dehydrogenase (DPD) (uracilemia ≥ 16 ng / ml) * Peripheral neuropathy\> grade 1 * Treatment with St. John's Wort * Treatment with yellow fever vaccine * Treatment with prophylactic phenytoin * Treatment with sorivudine or its chemically analogues related, such as brivudine * Active infection or other serious underlying disease likely to prevent the patient from receiving treatment * Persons deprived of their liberty, or under measure of judicial protection (curatorship or guardianship) or incapable of giving their consent * Impossibility of submitting to the medical follow-up of the test for geographical, social or psychological reasons.