The investigators compare two-week course of chemoradiation (33 Gy in 10 fractions with oral capecitabine) and conventional chemoradiation (50.4 Gy in 28 fractions with 5-FU and leucovorin) in this randomized trial.

1.1 experimental arm Two-week course concurrent chemoradiotherapy

• Radiotherapy, 33 Gy/10 fractions for 2 weeks

  ↓↓↓↓↓ ↓↓↓↓↓ Radical surgery 6 weeks after completion of chemoradiotherapy D1----------------------D12

• Capecitabine 825 mg/m2, twice daily

1.2 control arm

Standard concurrent chemoradiotherapy (CRT)

• Radiotherapy, 50.4 Gy/28 fractions for 6 weeks

  ↓↓↓↓↓ ↓↓↓↓↓ ↓↓↓↓↓ ↓↓↓↓↓ ↓↓↓↓↓ ↓↓↓ Radical surgery D1--------------------------------------------------------------------------D38

• Bolus 5-FU, 400 mg/ m2 and leucovorin, 20 mg/ m2 during week 1 and 5

• Capecitabine, 825 mg/ m2, bid

Inclusion Criteria:

1. histologically confirmed adenocarcinoma;
2. distal margin of the tumor located < 10 cm from the anal verge;
3. cT3-4N0-2 classification as determined by magnetic resonance imaging (MRI) and/or endorectal ultrasonography (EUS);
4. no evidence of distant metastasis;
5. Karnofsky performance score over 70;
6. adequate bone marrow, liver, and renal function (leucocytes >4000/mm3, hemoglobin >10 g/dL, platelets >100,000/mm3; serum bilirubin <1.5 mg/dL, serum transaminase <2.5 times the upper normal limit; serum creatinine <1.5 mg/dL).

Exclusion Criteria:

1. Metastatic disease
2. No complete resection of tumor (R2)