Clinical Research Directory

ICT consists of four or six two-weekly cycles of FOLFOXIRI. The dosages, dosage modification, and methods and schedule of administration of FOLFOXIRI follows the established treatment protocols and standard of care as prescribed in the Dutch Guidelines. It is administered as follows: * Day 1: irinotecan 165 mg/m2 body-surface area (BSA) intravenously (IV), followed by oxaliplatin 85mg/m2 BSA IV in combination with leucovorin 400mg/m2 BSA, followed by: * Day 1-2: 3200 mg/m2 BSA of continuous 5-fluorouracil IV * Day 3-14: rest days.

The dosages, dosage modification, and methods and schedule of administration of CAPOX follows the established treatment protocols and standard of care as prescribed in the Dutch Guidelines. CAPOX is administered as follows: * Day 1: Oxaliplatin 130 mg/m2 body-surface area \[BSA\], intravenously \[IV\]. * Day 1-14: Capecitabine 1000 mg/m2 BSA, orally, twice daily. * Day 15-21: Rest days. This regimen is initially administered for three cycles. In case of responsive or stable disease, a 4th cycle of CAPOX will be administered. In case of unacceptable toxicity (physician's discretion) to oxaliplatin, CAPOX may be continued as FOLFOX.

FOLFOX is a combination chemotherapy regimen, consisting of: * 5-fluorouracil (chemical name: L01BC02; trade name: 5-Fluorouracil; formulation: concentrate for solution for injection) * Oxaliplatin (chemical name: L01XA03; trade name: Oxaliplatin Accord; formulation: concentrate for solution for injection) FOLFOX is a well-established chemotherapy combination regimen for colorectal cancer, and is authorised for its intended use in this study. All FOLFOX component agents will be sourced from commercially available hospital stock and prepared according to standard protocols at participating centres.

In accordance with established standard-of-care protocols, chemoradiotherapy will commence 3-6 weeks after the completion of ICT, following restaging imaging and MDT review. The standard chemoradiotherapy regimen consists of external beam radiotherapy 50Gy in fractions of 2 Gy or 50.4 Gy in fractions of 1.8Gy combined with concomitant capecitabine, administered in accordance with Dutch Guidelines: * Dosage: 825 mg/m² Body Surface Area (BSA), twice daily * Route of administration: orally * Schedule: administered on all radiotherapy days * Treatment duration: 25 days In the case of cardiotoxicity or severe hand-foot syndrome due to capecitabine, treatment may be switched to Teysuno, in accordance with the Dutch guideline. The recommended dose of Teysuno in combination with oxaliplatin is 25 mg/m² body surface area, administered twice daily.

In patients with an incomplete response and resectable disease after first restaging, surgery is performed according to standard of care by a surgical oncologist with experience in rectal cancer surgery within 10-14 weeks after completion of chemoradiotherapy. The type and extent of the surgery is left to the discretion of the operating surgeon. In case of need for reconstructive surgery, the required specialist will be consulted and will attend the surgical procedure. The addition of IORT will be left to the discretion of the surgeon.

When a cCR is achieved after neoadjuvant therapy, patients may opt for a W\&W approach. A cCR is confirmed by imaging, endoscopy and digital rectal examination. Patients will receive a close surveillance follow up scheme according to the standard of care and local guidelines (51-54). Conduct follow-up every 3 months in the first year, every 6 months in the second year, and every 6 to 12 months in years 3 to 5, consisting of MRI and endoscopic evaluation. If any changes to the scar are detected during follow-up, a biopsy should be performed.