A paraneoplastic phenomenon is a disease or symptom that is the consequence of the presence of cancer in the body, but is not due to the local presence of cancer cells. A large number of these phenomena are mediated by the immune system.

Examples of paraneoplastic phenomena:

• Lambert-Eaton myasthenic syndrome (LEMS) in small-cell lung cancer
• Hypercalcemia in breast cancer and lung cancer due to the production of PTHrP (Parathyroid hormone-related protein)
• Granulocytosis (increased granulocytes) due to the production of G-CSF