Depends. Paraneoplastic syndrome is a syndrome (constellation of symptoms of variable types) that occurs in association (para-) with cancer (-neoplastic). Some specialized testing can detect antibodies involved in paraneoplastic syndrome, but sometimes it is not detectable. The body parts effected depends on the type of syndrome but may involve the entire body -- eg myasthenia gravis and thymoma.
Many sites. Paraneoplastic disorders usually arise from a tumor secreting hormones, peptides, or cytokines affecting other tissue sites . It can affect diverse organ systems, most notably the endocrine, neurologic, dermatologic, rheumatologic, and hematologic systems. The most common malignancy to be found includes small cell lung cancer, breast cancer, and hematologic malignancies. Treatments includes removal of the primary tumor and immunosuppression for neurologic, dermatologic, and rheumatologic syndromes.