• Histologically confirmed diagnosis of adenocarcinoma of the rectum

• Age ≥ 18 years

• ECOG performance status 0-1

• cT2-T3N0 or cT1-3N1 or cT4 or cN2

• Rectal cancer amenable to total mesorectal excision

• No evidence of distant metastases

• No prior pelvic radiation therapy

• No prior chemotherapy or surgery for rectal cancer

• Total neoadjuvant therapy (short course radiotherapy followed by consolidative chemotherapy) is allowed

• No infections requiring systemic antibiotic treatment

• Hgb \>8.0 gm/dL, PLT \> 150,000/mm3, total bilirubin ≤ 1.5x upper limit of normal, AST ≤ upper limit of normal, ALT ≤ 3x upper limit of normal

• Patients must read, agree to, and sign a statement of informed consent prior to participation in this study. Patients who do not read or understand English or eligible but must have the consent form read to them in its entirety by an official translator. Informed consent for non-literate or non-English speaking patients may not be obtained by using a relative or a member of the patient's clinical team as a translator.

• Female participants or reproductive potential, defined as not surgically sterilized and between menarche and 1 year post menopause, must have a negative serum pregnancy test within 4 weeks prior to initiation of study treatment.

• Women with childbearing potential who are negative for pregnancy (urine or blood) and who agree to use effective contraceptive methods. A woman of childbearing potential is defined by one who is biologically capable of becoming pregnant. Reliable contraception should be used from trial screening and must be continued throughout the study.