Fig. 1.

Host cells and niches that compose the PCa tumor microenvironment (TME). Multiple immune cells such as T regulatory (Treg), T helper IL-17-expressing cells (Th17) and macrophages (Mϕ) contribute to the TME. The vascular microenvironment composed of endothelial cells and their circulating progenitors provides nutrition to PCa cells. The bone microenvironment houses osteoblasts (OB) that provide a site for PCa cells to seed to and produce factors that regulate PCa proliferation. Fibroblasts located in both the prostate itself and at multiple metastatic sites produce a variety of factors that promote PCa growth and invasion