Myeloid cells: Prime drivers of tumor progression

Metastasis is a key step in cancer progression, and was traditionally attributed to the accumulation of genetic and epigenetic changes within individual cancer cells. These changes promoted invasiveness, immune evasion and survival at distant sites. However, recent studies reveal that metastasis is not achieved by the cancer cell in isolation, but requires intervention from the immune system. The myeloid cell population in particular is now implicated in many aspects of metastasis. Here, we bring together the evidence for the importance of various myeloid cell sub-populations throughout the metastatic process, from initiation of cancer cell invasiveness, to priming the tissue site for colonization.