CXCR4 and malignant peripheral nerve sheath tumor: Additionally, hematopoietic cells, including macrophages, have begun to emerge as an important signal for MPNST transformation and survival.25,26 Furthermore, autocrine loop signaling pathways such as CXCR4/CXCL12 have been implicated in progression of MPNST.27 Given these findings, a complex network between a diverse number of cells and signaling pathways is necessary for the development, maintenance, and progression of MPNST.