Standard therapy for localized rectal cancer includes chemotherapy and radiation therapy, followed by a "recovery" period of 7-12 weeks, surgery and adjuvant chemotherapy for 3-6 months. Even though this protocol achieves high cure rates, many patients need a rectal amputation with placement of definitive colostomies. About 10-20% of patients have a complete clinical response to chemo-radiation and no tumor can be found in the surgical specimen. These patients can be followed with close surveillance and avid surgery. The aim of this study is to evaluate if a strategy including the use of a highly active chemotherapy called "FOLFIRINOX" during the 12 weeks between the end of radiation therapy and evaluation for surgery increases the rates of complete response and, therefore, allows more patients to undergo non-surgical management.

Adult patients with locally advanced rectal cancer who have completed conventional long-course chemo-radiation of 54Gy with capecitabine will be randomized 1:1 to a total neo-adjuvant therapy (TNT) protocol or to a control group. Patients in the TNT arm will receive 4 cycles of interval chemotherapy with FOLFIRINOX (5-FU, irinotecan, oxaliplatin) between the end of chemo-radiation and re-staging and those in the control group will undergo standard post-radiation care during this period. All patients will be re-staged with colonoscopy and pelvic MRI 12 weeks after the end of chemo-radiation. Those with a complete clinical response will be placed under a watch-and-wait protocol with digital rectal examinations every 2 months and pelvic MRI and sigmoidoscopy every 6 months. Those wih residual tumors will undergo resection with total mesorectal excision (TME). Patients with a "near complete response", as defined by a multidisciplinary tumor board, will be re-staged at week 16 or 18 after chemo-radiation before undergoing surgery. Adjuvant chemotherapy will be done following the local standard of care.

Inclusion Criteria:

• Age >= 18 y/o
• Biopsy-confirmed rectal adenocarcinoma
• Tumor Stage T3+ or N+ M0
• Adequate liver function (total bilirubin < = 4.0)
• Adequate kidney function (calculate creatinine-clearance >=30ml/m2/min)
• Adequate bone marrow function (Platelet counts >=90.000, hemoglobin >=8mg/dl, neutrophile count >= 1.500/cm3)
• Completed chemo-radiation with at least 54Gy and capecitabine 1650mg/m2/d

Exclusion Criteria:

• Prior tumor resection
• Prior radiation to the pelvis
• Prior chemotherapy for rectal cancer
• Life expectancy < 6 months
• Unfit for surgery
• Need for urgent/ immediate surgery

This is an open-label study