Onconeural versus paraneoplastic antigens?

A hallmark of naturally occurring tumor immunity is the aberrant expression of so called "onconeural antigens" or "paraneoplastic antigens". At present, these two terms are used as synonyms for proteins which are normally expressed only in neuronal tissues, but in the process of carcinogenesis, they can be detected in tumors located outside the nervous system. As neuronal tissues are immunopriveleged zones, expression of these proteins in tumor cells can induce an autoimmune response, which manifests in the generation of autoantibodies and/or specific cytotoxic T-cells. Whether or not such immune responses necessarily lead to paraneoplastic syndromes or to a beneficial antitumor response or both is not fully understood. In this review we comprehensively summarize recent literature on paraneoplastic antigens including the corresponding neurological syndromes. A unified classification is proposed with "onconeural antigens" as collective term and a number of subgroups including the recently discovered cancer-retina antigens. Certain onconeural antigens can serve as paraneoplastic antigens under conditions which have yet to be defined, implying that the paraneoplastic function is not inherent to the antigen. The potential of onconeural antigens in cancer diagnostics and treatment strategies is discussed.