Fig. 1

Microglia crosstalk with metastatic cancer cells in the complex brain microenvironment. A Melanoma, lung and breast cancers have the highest risk to metastasize to the CNS. These panels summarize the main microglia alterations observed in these metastases to the CNS and their impact on the metastatic cancer cell-microglia cross-talk. B Upon cancer cell arrival in the brain, microglial cells will be attracted and recruited to the tumor site. According to the microenvironment context, microglia can differentiate into the M1 pro-inflammatory phenotype (to upregulate pro-inflammatory cytokines and to exert their anti-tumor response against metastatic cells), or into the M2 suppressive phenotype (to upregulate anti-inflammatory cytokines, to promote tumor survival and growth, and to strengthen the metastatic niche). Microglial cells might also present an intermediate M1-M2 phenotype