Capecitabine, Oxaliplatin, and Radiation Therapy in Treating Patients Who Are Undergoing Surgery for Stage I Rectal Cancer

Patient must have an Eastern Cooperative Oncology Group (ECOG)/Zubrod status of =< 2 Patient must have histologically confirmed invasive adenocarcinoma of the rectum; Note: patients with rectal tumors suspicious for invasion also are eligible Distal border of the patient's tumor must be within 8 cm from the anal verge as measured on endoscopic exam Patients with tumors fixed to adjacent structures on digital exam are NOT eligible Patient must have an uT2uN0 tumor, as confirmed by endorectal ultrasound (ERUS) or endorectal coil magnetic resonance imaging (MRI) scan; patients with uT1, uT3, or uT4 tumors are NOT eligible; greatest diameter of tumor cannot exceed 4 cm Patients with positive perirectal nodes on ERUS examination are NOT eligible Patients with histologic evidence of metastatic invasion of inguinal lymph nodes are NOT eligible Patients with the following conditions are NOT allowed on study: Metastatic disease or other primaries (patient must have had chest X-ray/computed tomography [CT] and abdominal & pelvic CT/MRI with IV contrast, as well as a colonoscopy) Previously documented history of familial adenomatous polyposis Previously documented history of hereditary non-polyposis colorectal cancer diagnosed clinically (Amsterdam II criteria) or by genetic testing History of inflammatory bowel disease History of prior radiation treatments to pelvis Clinically significant peripheral sensory or motor neuropathy (defined as symptomatic weakness, paresthesia or sensory alteration described to be interfering with function, interfering with activities of daily living, disabling or life-threatening) History of any clinically significant cardiac disease (i.e., class 3-4 congestive heart failure, symptomatic coronary artery disease, uncontrolled arrhythmia, and/or myocardial infarction within the last 6 months) History of uncontrolled seizures or clinically significant central nervous system disorders History of psychiatric conditions or diminished mental capacity that could compromise the giving of informed consent, or interfere with study compliance History of allergy and/or hypersensitivity to capecitabine and/or oxaliplatin History of difficulty or inability to take or absorb oral medications White blood cells (WBC) >= 3000/mm^3 Absolute neutrophil count (ANC) > 1,500/mm^3 Hemoglobin > 9.5 mg/dl Platelet count >= 100,000/mm^3 Total bilirubin =< 3 mg/dl Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase [SGOT]) and alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT]) =< 2.0 times institutional upper limit of normal (ULN) Alkaline phosphatase =< 2.0 times ULN Creatinine clearance (CLcr) >= 50 ml/min by Cockroft-Gault equation Patients who have experienced a prior malignancy must have received potentially curative therapy for that malignancy, and must be cancer-free for at least five years from the date of initial diagnosis (exceptions: patients treated for non-melanoma skin carcinoma, or in-situ carcinomas) Patients of reproductive potential must agree to use an effective method of birth control when undergoing treatments with known or possible mutagenic or teratogenic effects; all female participants of childbearing potential must have a negative urine or serum pregnancy test within two weeks prior to study registration