Non-Operative Management and Early Response Assessment in Rectal Cancer

Inclusion Criteria: * Diagnosis of biopsy proven stage I-IIIB (cT1-3, N0-2a, M0) adenocarcinoma of the rectum; staging must also be based on multidisciplinary evaluation including MRI * Tumor ≤ 12 cm from anal verge as determined by MRI or endoscopy * Clinically detectable (MR, endoscopy, or DRE) tumor present * Eastern Cooperative Oncology Group (ECOG) performance status 0-2 * At least 18 years of age * Adequate bone marrow function defined as: * Absolute neutrophil count (ANC) \> 1,500 cells/mm3 * Hemoglobin\> 8 g/dl * Platelets \>100,000 cells/mm3 * Women of childbearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control, abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while participating in this study, she must inform her treating physician immediately. * Able to understand and willing to sign an Institutional Review Board (IRB)-approved written informed consent document. Exclusion Criteria * Prior radiation therapy, chemotherapy or extirpative surgery for rectal cancer. * Prior oxaliplatin or capecitabine use for any malignancy * No prior radiation therapy to the pelvis. * A history of other malignancy (except non-melanomatous skin cancers) with the exception of malignancies for which all treatment was completed at least 2 years before registration and the patient has no evidence of disease. * Currently receiving any inves…