CXCL12 and colorectal cancer: In our previous study, senescent tumor cells were shown to play an important role in cancer progression: senescent tumor cells are actively involved in the collective invasion and metastasis via CXCL12/CXCR4 signaling.[9] In subsequent studies, we found that immune cells could not infiltrate tumor tissues and were located around senescent tumor cells in colorectal cancer (CRC).