CD74 and neoplasm: CD74‐positive microglia promote metastatic outgrowth by secreting MDK; targeted inhibition of the core regulator PI3K effectively halts TAM‐mediated tumor colonization [556].During the colonization phase, cathepsin S released by BM‐derived macrophages (MDMs) and tumor cell‐derived IL‐6 (which suppresses the anti‐inflammatory function of microglia via the JAK2/STAT3 pathway) play crucial roles [557, 558].