All three patients analyzed had cancer (2 × melanoma, with a lymph node metastasis in one of them; 1 × small cell lung cancer with lymph node metastases), suggesting that septin-3 IgG-associated autoimmune cerebellar ataxia may be a novel paraneoplastic neurological syndrome (PNS). Here, SEPTIN3 is linked to metastatic malignant neoplasm in the lymph nodes.