A case of IVIg responsive paraneoplastic SOX1 peripheral neuropathy in a male with breast carcinoma.

Abstract Background and aims SOX1 antibodies are generally associated with small cell lung cancer and anti-Hu antibody overlap is common. This case demonstrates isolated SOX1 antibodies with an uncommon tumor type, and relapse of a paraneoplastic syndrome with recurrence of tumor. Methods We describe a case of a 65-year-old male with a paraneoplastic peripheral neuropathy and SOX1 antibody positivity in the context of a prior male breast Grade 2 ductal carcinoma, in remission at the time of the initial neurological presentation. Results Treatment response to intravenous immunoglobulin (IVIg) was demonstrated. After period of clinical stability on IVIg in the context of remission of breast cancer, the patient experienced a relapse of his neuropathy. This was found to be associated with tumor recurrence and again responded to tumor excision, radiotherapy and IVIg. Interpretation Male breast cancer has not previously been associated with SOX1 antibody positive paraneoplastic neuropathy.