Osteosarcoma-derived exosomes enriched in miR-21 and miR-34a—often accompanied by miR-181a/miR-222/miR-146a—activate Schwann cells (via ERK–c-Jun) to secrete guidance cues and proNGF/GFRα1, stimulating neurite extension; in immune cells, exosomal miR-21 targets PTEN/PDCD4 and miR-146a modulates TRAF6–NF-κB to skew TAMs toward suppressive states, while Schwann-cell CCL2/CXCL5 recruits CCR2+ myeloid populations that stabilise the neuro-immune niche (67, 68). The gene discussed is GFRA1; the disease is osteosarcoma.