Interest of PET-MRI in the Evaluation of the Response After Neoadjuvant Treatment of Locally Advanced Rectal Adenocarcinoma

The management of localized rectal cancer is done in two phases. The first phase, medical, combines a possible first chemotherapy, followed by a concomitant chemoradiotherapy. The second phase, 6 to 8 weeks later, consists of surgery of the rectum.

Magnetic resonance imaging (MRI) of the pelvis allows staging of the tumor and its possible lymph node extensions. MRI can also be used to assess tumor response after the first phase of treatment and before surgery. But MRI of the pelvis is partially imperfect.

PET-MRI is an examination that combines MRI with an injection of [18 F]fluorodeoxyglucose (18F-FDG). It is known to be more sensitive in assessing tumor stage and lymph node extensions compared to MRI and more sensitive in assessing tumor response before surgery.

The aim of this study is to determine predictive parameters for response to the first phase of treatment by accurately identifying the characteristics of tumors that have responded or not to treatment with chemotherapy and chemoradiotherapy.

Inclusion criteria

• World Health Organization (WHO)/Eastern Cooperative Oncology Group (ECOG) 0 to 2
• Histologically proven rectal cancer
• clinical tumor classification (cT) : cT3 - cT4 or all T / N+ / M0
• Tumor resectable or considered resectable after chemoradiotherapy
• Decision chemotherapy followed by neoadjuvant chemoradiotherapy decided at the organ Multidisciplinary Meeting
• Absence of distant metastases
• Adequate contraception for women of childbearing potential
• Free, signed and informed consent
• For women of childbearing potential : negative pregnancy test

Exclusion criteria

• Subject with Uncontrolled diabetes
• Contraindication to surgery
• Contraindication to MRI
• Contraindication to PET scan
• Contraindication to chemotherapy
• History of pelvic radiotherapy
• History of major co-morbidity that may prevent treatment and no active infection (HIV or chronic hepatitis B or C)
• Colloid (mucinous) adenocarcinoma
• Presence of distant metastases
• Contraindication to 5-FluoroUracil (FU), oxaliplatin or irinotecan
• History of known Gilbert's disease
• Patient with known UGT1A1 genotype
• Known Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency
• Medical history of chronic diarrhea or inflammatory disease of the colon or rectum
• Medical history of angina or myocardial infarction.
• Active progressive infection or any other serious medical condition that could compromise the administration of the treatment
• Other concurrent cancer, or medical history of cancer other than treated in situ cervical carcinoma or basal cell carcinoma or squamous cell carcinoma
• Patient enrolled in another clinical trial testing an investigational agent
• Pregnant or breastfeeding woman
• Persons deprived of their freedom or under guardianship or incapable of giving consent
• Any psychological, familial, sociological or geographic condition that may interfere with the study protocol or follow-up schedule