found that ultra‐small copper selenide nanoparticles (Cu2‐xSe, also denoted as CS NPs) could significantly promote M2‐to‐M1 polarization and obviously inhibit the progression and recurrence of B16F10 tumor via a novel ROS‐mediated macrophage polarization mechanism (Figure 9).[189] The CS NPs could robustly enhance ROS level in macrophages, which facilitated the auto‐ubiquitination of TRAF6 and then induce TRAF6 downstream factor IRF5 activation. Here, IRF5 is linked to neoplasm.