Immune-mediated paraneoplasia

Cancers induce a loss of homeostasis through the uncontrolled production and release of a variety of biologically active cellular products, natural compounds produced in unnatural quantities within abnormal anatomical locations. Often, there is an immune response to which the cancerous growth may succumb, or have the characteristics required to survive. If, during its proliferation, the cancer should coincidentally express a potent autoantigen then the organ in which that antigen is normally located may be damaged by the resultant immune response. Paradoxically, this aberrant immunological activity rarely has any appreciable inhibitory effects on the causal cancer. This inconsistency may result from the cancer's ability to block the host's immunological activity, while the affected organ situated elsewhere has no such capacity. Some predisposition, such as trauma to the affected organ, may prove a prerequisite that provides access to hitherto immunologically privileged sites. The effects of the subsequent loss of tolerance are often the first indication of a health problem, prompting the patient to seek medical help. Immune-mediated paraneoplasia is identified by antibody activity with any of a small but growing collection of organ-specific antigens demonstrated to have a distinct disease association and an apparent involvement in autoimmunity. Examples of the most common are described as introduction to this unusual collection of autoimmune diseases, for which in some cases the cause is known, and these may provide insight into the cause of those that are not.