CXCL12 and colorectal cancer: At present, it has been found that CXCL12/CXCR4 axis can play an important role in the occurrence, development and metastasis of many kinds of human tumors, including breast cancer, gastric cancer, colorectal cancer, prostate cancer, renal cell carcinoma, ovarian cancer and so on [8, 9], especially in the biological behaviors such as proliferation, adhesion, migration, invasion and metastasis of tumor cells [10].