Figure 7.

A proposed mechanistic model of 27-HC and M2 type macrophages in the tumor microenvironment. 27-HC secreted by macrophages promotes breast cancer cell proliferation and stimulates macrophages themselves to secrete chemokines, such as CCL2, CCL3 and CCL4, which further promote the CCR2⁺ and CCR5⁺ monocytes to migrate to tumor sites. The infiltrated monocytes can be polarized to M2 type macrophages with a stronger 27-HC secreting capacity partly by exosomes derived from breast tumor cells. Breast cancer cells may also contribute to 27-HC accumulation through down-regulating expression of CYP7B1 by hypermethylation in its promoter.