Paraneoplastic neurological syndromes (PNS) are immune-mediated disorders in which a tumor expresses onconeural antigens (proteins normally restricted to the nervous system), triggering cross-reactive antibodies and T-cells that attack both tumor and normal neural tissue. Key antibody-syndrome associations include anti-Hu (ANNA-1) with small cell lung cancer causing sensory neuropathy and encephalomyelitis, anti-Yo (PCA-1) with ovarian/breast cancer causing subacute cerebellar degeneration, anti-NMDA receptor with ovarian teratoma causing limbic encephalitis with psychiatric symptoms, and anti-amphiphysin with breast cancer causing stiff person syndrome. PNS often precede cancer diagnosis by months to years, making neurological symptom recognition critical for early tumor detection.