Plasma cell myeloma (PCM) is an essentially incurable neoplastic disorder of terminally differentiated B cells. The neoplastic clone usually secretes a monoclonal protein in the serum or urine (the ‘M band’). About 20% of PCM secrete light chains only, which are detectable in the urine as Bence Jones protein. The clinical picture is one of bone marrow failure, due to infiltration of the marrow by malignant plasma cells; renal failure due to damage to renal tubules by the excess light chains and pain due to lytic lesions of the bones. The outcome remains poor with median survival of 5 years.