CXCR4 and cancer: 178, 179. Additionally, chemokine CXCL12 produced by perivascular fibroblasts can attract CXCR4+ TAMs together with mobile cancer cells toward blood vessels. After tumor cells enter the circulation, migratory TAMs differentiate into perivascular macrophages (primarily M2), increasing vascular permeability and supporting tumor-cell intravasation 179, 180.