This study is being done to evaluate if by adding a 3rd drug (irinotecan) to the standard regimen of FOLFOX or CAPOX given following long-course chemoradiation for patients with locally advanced rectal cancer can increase the clinical complete response rate (tumor disappears by exam, endoscopy, and imaging).
The usual approach for patients who are not in a study is treatment with chemoradiation followed by radical surgery then possibly chemotherapy after surgery, or a combination of chemotherapy then chemoradiation then radical surgery.