GZMA and neuroblastoma: NK cells secreted exosomes containing typical NK markers and cytotoxic proteins (e.g., perforin molecules, Fas ligand, granzyme A & B (GzmA & GzmB), and granulysin), which mediated cytotoxicity against different solid tumours (e.g., breast cancer and neuroblastoma), resulting in cytotoxicity of cancer cells [53–55] (Fig. 1a).