Table 1.

Outstanding questions

1) Why do some tumors preferentially colonize specific organs (e.g. brain)?

2) Is the microglia response to infiltrating metastatic cancer cells specific to the tumor type?

3) Is the microglia pro-inflammatory signature an anti-tumor immune response, or is it exploited by metastatic tumor cells to promote their colonization and growth in brain?

4) What are the microglia long-term effects on the metastatic disease progression?

5) Does cytokine level influence differently microglia in patient with CNS metastases compared with patients with CNS inflammatory diseases?

6) How can metastatic cancer cells escape the microglia surveillance and colonize the CNS microenvironment?

7) How do microglia respond to immune checkpoint-targeted therapy?