Implementation of a Tumor Response Assessment Program Integrating the Shared Medical Decision Into the Organ Preservation Strategy for Rectal Cancer Patients

Inclusion Criteria: * Patient aged 18 to 80 * Histologically proven lieberkuhnian adenocarcinoma with MSS status ; * Patient who has or is due to receive neoadjuvant treatment (4 to 6 courses of (m)FOLFIRINOX or FOLFOX chemotherapy + CAP 50 radiochemotherapy or CAP 50 radiochemotherapy alone); * BEFORE any neoadjuvant treatment: * Tumor classified T2T3 (on MRI) * N0-N1 (≤ 3 positive lymph nodes \* or size ≤ 8 mm) (on MRI) * \* positive node = node size \> 5 mm minor axis and/or morphologically suspicious appearance Tumor size ≤4 cm (ON MRI) * No distant metastasis (M0)\_ TAP scan or PET scan * ≤ 8 cm from anal margin (On MRI) (Clinical examination\*) \*if the clinical examination is not possible, then the source data is that of the MRI. * No invasion of the anal canal and/or sphincters (internal and external) (On MRI) * Operable patient * Ability to comply with the protocol and follow-up appointments (repeated assessment consultations and close follow-up if randomized to the Experimental Group); * Person affiliated with or benefiting from a social security scheme; * Free and informed consent signed by the patient. Exclusion Criteria: * Patients with a history of chemotherapy or pelvic irradiation (excluding neoadjuvant treatment) * Contraindication to pelvic MRI * Patients with MSI status undergoing immunotherapy * Other concomitant cancer or history of cancer within 5 years, with the exception of carcinoma in situ of the cervix or basal cell or squamous cell skin carcinoma or any other carcinoma in situ, considered cured * Women who are pregnant, likely to become pregnant, or who are breast-feeding; * Person under guardianship, curatorship or safeguard of justice, or person deprived of liberty. * Unable to undergo medical follow-up for geographical, social or psychological reasons.