Phase II/III Study to Assess the Efficacy of Neoadjuvant Consolidation Chemotherapy in Rectal Cancer Patients.

This is a Phase II/III randomized study involving non-metastatic rectal cancer patients who are candidates for neoadjuvant chemoradiotherapy. Eligible patients will be randomized between two treatment arms: Experimental arm: Long course CRT is followed by 4 cycles of combination chemotherapy of modified FOLFOX6 or 3 cycles of XELOX and then surgery. After surgery, patients with pT0-2 N0 will not receive adjuvant chemotherapy. Patients with higher pathological stage will receive adjuvant chemotherapy (4 cycles of modified FOLFOX6 or 3 cycles of XELOX). Standard arm: Long course CRT will be followed by surgery 10-12 weeks after the end of CRT. After surgery, patients with pT0-2 N0 will not receive adjuvant chemotherapy. Patients with higher pathological stage will receive adjuvant chemotherapy (8 cycles of modified FOLFOX6 or 6 cycles of XELOX). The study aims to assess the efficacy of consolidation chemotherapy given in the interval between the end of CRT and surgery to allow for early initiation of systemic therapy aiming to decrease distant relapse rate and enhancing pathological response.