Tailored Operative or Non-operative Management for Low-risk Rectal Cancer After Intensive Neoadjuvant Treatment

Inclusion Criteria:

* Age ≥18 years and ≤85 years
* ECOG Performance status 0-1
* Histologically confirmed diagnosis of adenocarcinoma of the rectum, with tumor differentiation Grade 1-3
* The distance from down verge of tumor to anal-rectal junction (ARJ) ≤8cm based on MRI, or ≤12cm based on sigmoidoscopy;
* Clinical Stage T2 or T3a or T3b and EMVI (-) and MRF (-) and extra-mesorectal metastatic lymph node (-) based on MRI
* No evidence of distant metastases
* No prior pelvic radiation therapy
* No prior chemotherapy or surgery for rectal cancer
* No active infections requiring systemic antibiotic treatment
* ANC \> 1.5 cells/mm3, HGB \> 10.0 g/dL, PLT \> 100,000/mm3, total bilirubin ≤ 1.5 x ULN, AST≤ 3 x ULN, ALT ≤ 3 x ULN.
* Patients must read, agree to, and sign a statement of Informed Consent prior to participation in this study.

Exclusion Criteria:

* Recurrent rectal cancer
* Primary unresectable rectal cancer. A tumor is considered unresectable when invading adjacent organs and an en-bloc resection will not achieve negative margins.
* Creatinine level greater than 1.5 times the upper limit of normal.
* Patients who have received prior pelvic radiotherapy.
* Patients who are unable to undergo an MRI.
* Patients with a history of a prior malignancy within the past 5 years, except for well treated basal cell cancer, squamous cell skin cancer, breast cancer, thyroid cancer or small renal cancer, and with DFS \>5 years.
* Patients with a history of any arterial thrombotic event within the past 6 months. This includes angina (stable or unstable), MI, TIA, or CVA.
* Other Anticancer or Experimental Therapy.
* Women who are pregnant or breast-feeding.
* Patients with any other concurrent medical or psychiatric condition or disease which would make them inappropriate candidates for entry into this study.