In addition, cases of paraneoplastic NMOSD have been reported increasingly frequently, and some case reports of patients with paraneoplastic NMOSD have shown the expression of AQP4 in the tumor cells, suggesting that AQP4 autoantibodies may be produced in the autoimmune response to AQP4 protein in the tumor cells of some paraneoplastic NMOSD patients [231,232,233]. Here, AQP4 is linked to neoplasm.