Are amphiphysin, CV2/CRMP5, and Yo antibodies linked to paraneoplastic neurologic syndromes without proving active cancer or causation?

Paraneoplastic neurologic syndromes (PNS) can precede recognition of cancer, making these antibodies clinically important signals—but not stand-alone diagnoses. The stated claim is strongly supported.

Clinical association and cancer implications

• Amphiphysin, CV2/CRMP5, and Yo/PCA-1 are high-risk PNS antibodies in the 2021 PNS-Care framework, a category associated with cancer in >70% of cases when the clinical setting is appropriate.
• Amphiphysin is associated with malignancy in approximately 80% of reported cases, particularly small-cell lung cancer (SCLC) and breast cancer, and may accompany stiff-person-spectrum disease, neuropathy, or encephalomyelitis.
• CV2/CRMP5 is associated with cancer in >80% of cases, chiefly SCLC and thymoma, across phenotypes including sensory neuronopathy, encephalomyelitis, cerebellar syndrome, optic neuritis, and peripheral neuropathy.
• Yo/PCA-1 is most characteristically associated with rapidly progressive cerebellar syndrome and breast or ovarian cancer; malignancy occurs in >90% in the guideline summary.

Diagnostic interpretation

• A positive result does not establish active cancer. PNS-Care classification ordinarily requires compatible clinical features plus cancer evidence.
• Assay confirmation matters: in one retrospective cohort, only 39% of antibody-positive patients had PNS; among 23 ultimately classified cases, 14 were false-positive antibody results after alternative diagnoses or absent malignancy were established. Isolated line-blot findings, including for Yo and CRMP5, require corroboration with tissue-based testing and a second antigen-specific assay.
• A credible result warrants targeted tumor evaluation and, when phenotype and antibody are high risk but initial screening is negative, consideration of periodic reassessment.

Mechanistic meaning

• These predominantly intracellular-antigen antibodies usually mark a tumor-directed immune response rather than proving direct antibody injury. CD8-positive cytotoxic T-cell injury is strongly implicated in CRMP5- and Yo-associated neuronal loss.
• Amphiphysin has experimental evidence for impaired inhibitory neurotransmission, but this does not establish antibody causation in an individual patient.

Bottom line

• These antibodies substantially raise suspicion for PNS and specific occult cancers, but seropositivity alone neither diagnoses current malignancy nor proves that the antibody itself is causing neurologic disease.