Clinical Study of Apatinib Combined With Second - Line Chemotherapy for Metastatic Colorectal Cancer

(1) Evaluate the efficacy of apatinib in combination with standard second-line chemotherapy for advanced colorectal cancer. Whether it can prolong Progression Free Survival (PFS), overall survival (OS) in patients with advanced colorectal cancer and reduce symptoms and improve quality of life compared with standard second-line chemotherapy; (2) Observe the safety of apatinib for the treatment of advanced colorectal cancer.