XELOX+Bevacizumab and XELIRI + Bevacizumab Alternative Regimen as First-line Treatment for Advanced Colorectal Cancer

Colorectal cancer will be resistant to Chemotherapy drugs after treated for a period of time .In the past, the classical treatment regiment was to change other drug after tumor progressed. In theory, the continuous use of such a drug could shortening the patient's drug resistance time. It has been shown that the alternate use of the two drug combinations is reasonable in clinical. This application can not only further improve the curative effect but also significantly reduce the side effects. So the investigators are going to carry out a prospective phase II clinical study. The control group change to second-line treatment after progression of first-line drugs. The experimental group use the first line and the second line,alternately, for every two cycles. The combination of bevacizumab is a first line development, and the second line can still be used . Objective to compare the clinical value of XELOX + bevacizumab and XELIRI + bevacizumab alternation regimen in the first-line treatment of advanced colorectal cancer.