Paraneoplastic Syndrome — Cancer-Related Immune Effects

Paraneoplastic syndromes represent non-metastatic systemic manifestations of malignancy. They arise through two primary pathogenetic mechanisms: aberrant humoral secretion of bioactive molecules (such as hormones, peptides, or cytokines) or autoimmune cross-reactivity. In autoimmune cases, the immune system generates antibodies against tumour antigens (onconeural antigens) that mistakenly cross-react with normal host tissues, particularly within the central and peripheral nervous systems.

These syndromes can affect almost any organ system, resulting in neurological, endocrine, haematological, dermatological, or renal disturbances. Crucially, paraneoplastic manifestations frequently precede the clinical detection of the primary tumour by months or years, serving as an important diagnostic signpost.

Because paraneoplastic syndromes often emerge before a tumour causes local symptoms, recognizing them can lead to earlier cancer detection and timely treatment. Conversely, severe paraneoplastic complications—such as autoimmune encephalitis, profound muscle weakness, or severe hypercalcaemia—can cause significant disability or life-threatening crises. Managing these symptoms rapidly is essential for safeguarding organ function and allowing patients to undergo cancer-directed therapy safely.

Diagnosis involves testing for specific onconeural autoantibodies in the blood or cerebrospinal fluid (such as anti-Hu, anti-Yo, or anti-Ri). Endocrine syndromes are evaluated through hormone profiles, including serum calcium, parathyroid hormone-related protein (PTHrP), and electrolytes. Extensive radiological imaging—including whole-body PET-CT scans—is routinely performed to identify the occult primary tumour driving the syndrome.

Paraneoplastic syndromes are most frequently linked with small cell lung cancer (SCLC), which has high neuroendocrine activity. Other commonly associated cancers include thymoma, breast cancer, ovarian cancer, non-Hodgkin lymphoma, and renal cell carcinoma. Examples include Lambert-Eaton myasthenic syndrome, syndrome of inappropriate antidiuretic hormone secretion (SIADH), and humoral hypercalcaemia of malignancy.

The most definitive treatment for a paraneoplastic syndrome is the eradication of the underlying tumour using surgery, chemotherapy, or radiotherapy. Alongside tumour-directed therapies, symptomatic treatments are vital. Autoimmune paraneoplastic conditions frequently require immunomodulatory therapies, such as high-dose corticosteroids, intravenous immunoglobulin (IVIG), or plasma exchange. Endocrine disruptions are managed with specific metabolic stabilisers, such as bisphosphonates for hypercalcaemia.