This is a study that compares two types of surgery for rectal cancer. There are two procedures that can be used during this surgery, conventional abdominal resection (APR) and extended (or extralevator) APR. The investigators are doing this research to see whether the extralevator APR increases the likelihood that the edge of the tissue that is removed will be more likely to be free from cancer cells compared with the conventional APR surgery. At this time there is no evidence that one type of procedure is better at this than the other. The objective of this research is to determine whether extralevator APR is more likely to have clean margins (free of cancer) compared to the standard APR surgery.

Inclusion Criteria:

• Resectable, histologically proven primary adenocarcinoma of the low rectum with internal and/or external sphincter muscle involvement. Staged as follows prior to neoadjuvant chemoradiation:
• Stage T3 or T4 at MRI
• N0-2 at MRI
• M0 at CT scan
• Patient must undergo long term neoadjuvant chemoradiation: 20 fractions of radiation over ≥5 weeks: total of 50-60 Gy, and chemotherapeutic agents

Exclusion Criteria:

• Squamous cell carcinoma
• Adenocarcinoma Stage T1-2, any N
• T4 with one of the following:

with pelvic side wall involvement requiring sacrectomy requiring prostatectomy (partial or total) Distant metastasis (M1) Unresectable primary rectal cancer or Inability to complete R0 resection. Recurrent rectal cancer Previous pelvic malignancy Inability to sign informed consent Pregnancy