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.