Rechallenge of Prior Regimen in Third or Later-line Chemotherapy in Metastatic Colorectal Cancer

XELOX regimen: Oxaliplatin 130mg/m2, intravenous, on day 1; Capecitabine 1000mg/m2, oral, twice daily, continuously for 14 days; ±bevacizumab 7.5mg/kg, intravenous, on day 1; repeating every 3 weeks. FOLFOX regimen: Oxaliplatin 85mg/m2 on day 1; Calcium folinate 400mg/m2 on day 1; 5-FU 400mg/m2 on day 1; 5-FU 2.4g/m2, continuous intravenous infusion for 46 hours, ± Bevacizumab 5mg/kg or ± Cetuximab 500mg/m2, repeating every 2 weeks. FOLFIRI regimen: Irinotecan 180mg/m2 on day 1; Calcium folinate 400mg/m2 on day 1; 5-FU 400mg/m2 on day 1; 5-FU 2.4g/m2, continuous intravenous infusion for 46 hours; ± Bevacizumab 5mg/kg or ± Cetuximab 500mg/m2, repeating every 2 weeks. Irinotecan monotherapy regimen: Irinotecan 180mg/m2 on day 1, ± Bevacizumab 5mg/kg or ± Cetuximab 500mg/m2, repeating every 2 weeks. Raltitrexed contained regimen: Raltitrexed 3mg/m2 on day 1; ± Bevacizumab 7.5mg/kg, repeating every 3 weeks; Raltitrexed 2mg/m2 on day 1; ± Cetuximab 500mg/m2, repeating every 2 weeks.