Do amphiphysin, CV2/CRMP5, and Yo antibodies need cancer-context interpretation?

High-risk onconeural antibodies can be clinically important signals of tumor-associated autoimmunity, but their value depends on both assay validity and the neurologic/cancer context. For a 77-year-old man, CV2/CRMP5 in particular may focus attention on small-cell lung cancer or thymoma; antibody-specific associations should guide—not replace—evaluation.

Cancer-context interpretation

• Amphiphysin, CV2/CRMP5, and Yo/PCA-1 are classified as high-risk antibodies in the 2021 PNS-Care framework, each associated with cancer in >70% of relevant cases.
• Typical associations are amphiphysin with small-cell lung or breast cancer; CV2/CRMP5 with small-cell lung cancer or thymoma; and Yo with breast or gynecologic, particularly ovarian, cancer.
• These intracellular-antigen antibodies primarily mark a tumor-linked, T-cell-mediated immune response rather than proving direct antibody-mediated injury.

Why a positive result is not diagnostic

• A positive antibody result does not establish either active cancer or paraneoplastic neurologic syndrome (PNS). PNS-Care requires a compatible neurologic syndrome, cancer assessment, antibody risk category, follow-up, and exclusion of plausible alternatives.
• Commercial line blots can yield clinically discordant positives, particularly for Yo and CV2/CRMP5. In one cohort, PNS was present in 8% with line-blot-only antibodies versus 91% with concordant line blot plus rat-brain immunohistochemistry; 12/13 isolated Yo-positive results lacked PNS.
• In another cohort, only 31% of discordant serum-only positives were clinically relevant. Yo immunoblot positive predictive value was 28.8% alone, improving to 77.8% after immunofluorescence confirmation.

Clinical implications

• Unexpected, low-titer, serum-only, or phenotype-discordant results warrant confirmation with complementary tissue-based immunohistochemistry/immunofluorescence and antigen-specific testing, ideally in a reference laboratory.
• If a high-risk phenotype and confirmed high-risk antibody are present but initial tumor screening is negative, repeat screening every 4–6 months for 2 years is recommended.

Bottom line

• These antibodies justify prompt, targeted cancer and neurologic evaluation, but neither antibody positivity nor a screening-assay result alone diagnoses active malignancy or PNS.