S1PR1 and colorectal carcinoma: Mechanistically, sphingosine-1-phosphate receptor 1 (S1PR1)–STAT3 signalling in CRC cells results in the production of IL-6 to induce the activation of S1PR1 and p-STAT3 in MDSCs, thus leading to the formation of a PMN in the liver to promote CRLM [190].