M-protein is manufactured (synthesized) by malignant plasma cells (or myeloma cells). The amount of protein produced and released into the serum (the liquid part of the blood that is left after the blood cells are removed), and sometimes into the urine, reflects the amount of myeloma present in the body at any given time. This protein, which is released into the serum or urine, is called a serum or urine tumor marker.
Only a very few cancers have this type of a marker which, in this case, makes it possible to assess the amount of myeloma at the time of initial diagnosis and track the amount of myeloma throughout the course of the disease. One can look at response to treatment, depth of remission, and, if necessary, the patient’s relapse using exact numbers, which is a unique advantage.