S100A9 and posterior cortical atrophy: Finally, in an in vivo study, small vesicles from PCa have been demonstrated to promote the recruitment of MDSC cells into the TME, by increasing the expression of the chemokine receptor 4 (CXCR4) [64]; on the other hand, MDSC-derived sEV-carried S100A9, a calcium-binding protein with proinflammatory/protumoral properties, has been found to increase castration-resistant PCa aggressiveness via the circMID1/miR-506-3p/MID1 cascade [65].