Põlajeva et al. (33) propose that the accumulation of mast cells (MCs) in GBM tumors might be related to the levels of stem cell factor and the chemokine CXCL12; Attarha et al. (34) demonstrate that MCs respond to multiple signals in a glioma grade-dependent manner to infiltrate mouse and human gliomas and induce the differentiation of glioma cells. Here, CXCL12 is linked to glioma.