The Bence-Jones Protein (BJP) test detects abnormal monoclonal light chains in urine, primarily used to diagnose and monitor blood cancers like Multiple Myeloma, other plasma cell disorders, and conditions like amyloidosis. Performed on a urine sample (often 24-hour collection or random), it uses techniques like electrophoresis or immunoassay, indicating cancerous plasma cells producing excess light chains that spill into urine, helping stage cancer and assess treatment