Inspired by previous reports suggesting a paraneoplastic etiology in rare cases of cancer-associated NMOSD [11–22], this is the first study systematically investigating the seroprevalence of onconeural antibodies (anti-Hu, Yo, Ri, CV2/CRMP5, Ma1, Ma2, Zic4, SOX1, Tr, and amphiphysin) in NMOSD patients. Here, SOX1 is linked to cancer.