Capecitabine and Oxaliplatin or Standard Follow-Up Care in Treating Patients Who Have Undergone Surgery for Locally Advanced Rectal Cancer

DISEASE CHARACTERISTICS:

* Histologically confirmed adenocarcinoma of the rectum

  * Within 15 cm of the anal verge
  * Locally advanced disease
* Underwent complete resection of primary tumor within the past 12 weeks

  * ypT0-4, N0-2 with definitive histology at surgery
  * Circumferential resection margin \> 1 mm
  * No gross evidence of residual disease
* Received neoadjuvant fluoropyrimidine-based chemoradiotherapy with ≥ 45 Gy planned total radiation dose, given in 1 of the following fashions:

  * Prolonged fluorouracil IV during radiotherapy
  * Low-dose leucovorin calcium and fluorouracil (days 1-5 and 29-33) concurrently with radiotherapy
  * Oral capecitabine concurrently with radiotherapy
* No evidence of metastatic disease

PATIENT CHARACTERISTICS:

* WHO performance status 0-1
* Absolute neutrophil count ≥ 1,500/mm³
* Platelet count ≥ 100,000/mm³
* Creatinine clearance ≥ 50 mL/min
* Bilirubin ≤ 1.25 times upper limit of normal (ULN)
* AST and ALT ≤ 1.25 times ULN
* Not pregnant or nursing
* Negative pregnancy test
* Fertile patients must use effective contraception during and for ≥ 3 months after completion of study treatment
* No known dihydropyrimidine dehydrogenase deficiency
* No hypersensitivity to platinum compounds
* No preexisting peripheral neuropathy ≥ grade 1
* No lack of physical integrity of the upper gastrointestinal tract
* No malabsorption syndrome
* No other serious uncontrolled medical condition or concurrent medical illness that would compromise life expectancy and/or preclude study compliance, including any of the following:

  * Serious uncontrolled infections
  * Significant cardiac disease (e.g., uncontrolled angina, congestive heart failure, cardiomyopathy, or arrhythmias) or myocardial infarction within the past 12 months
  * Interstitial pneumonia or symptomatic lung fibrosis
* No other malignancies except adequately treated in situ carcinoma of the cervix or basal cell or squamous cell carcinoma of the skin, unless disease-free for ≥ 10 years
* No history of uncontrolled seizures, CNS disorders, or psychiatric disability that would preclude study compliance

PRIOR CONCURRENT THERAPY:

* See Disease Characteristics
* No prior chemotherapy exceeding 6 weeks in duration

  * Prior chemotherapy given as part of neoadjuvant treatment (i.e., chemoradiotherapy) may last a maximum of 11-12 weeks
* No prior oxaliplatin
* Prior mitomycin C, irinotecan hydrochloride, or cetuximab allowed
* No concurrent warfarin, antiviral agents, or phenytoin