Multiple myeloma is a cancer that originates in the bone marrow, specifically affecting plasma cells, a type of white blood cell. Plasma cells are normally part of the immune system and produce antibodies (immunoglobulins) to fight infections. In multiple myeloma, cancerous plasma cells multiply uncontrollably. This leads to the excessive production of a specific protein that can be detected in the blood and urine.
The Monoclonal Protein M-Spike
The elevated protein in multiple myeloma is a Monoclonal Immunoglobulin, often referred to as the M-protein, M-component, or paraprotein. When measured in a blood test, this protein creates a distinct, sharp peak on the results graph, known as the M-spike. The M-protein is an abnormal antibody produced by malignant plasma cells (typically Immunoglobulin G or Immunoglobulin A). This protein represents a massive overabundance of a single, identical type of antibody produced by a cancerous clone. These abnormal antibodies are typically non-functional, meaning they do not effectively contribute to the body’s defense against pathogens.
The Origin of Excessive Protein Production
The root of this protein overproduction lies in the function of plasma cells, which are specialized white blood cells residing primarily in the bone marrow. Healthy plasma cells produce a wide variety of antibodies, known as a “polyclonal” response, to protect against numerous infections. In multiple myeloma, a single, abnormal plasma cell begins to replicate uncontrollably, creating an overwhelming population of identical cancerous cells (myeloma cells). Since all these myeloma cells originate from the same source, they produce the exact same protein—the monoclonal protein. This excessive protein is a waste product whose buildup can cause complications such as thickening the blood or damaging the kidneys, while the cell growth crowds out the bone marrow.
Clinical Detection and Disease Monitoring
The detection and measurement of the M-protein are central to the diagnosis and management of multiple myeloma. Several laboratory tests are used to find and quantify the M-protein in the blood and urine:
- Serum Protein Electrophoresis (SPEP) separates proteins in the blood serum and visually detects the M-spike.
- Urine Protein Electrophoresis (UPEP) detects the protein if it is being filtered through the kidneys.
- Serum Free Light Chains (FLC) measures parts of the antibody structure produced in excess without the heavy chain.
The FLC assay is particularly useful when M-protein levels are too low to be reliably measured by SPEP. These tests are used for initial diagnosis and routine monitoring to determine treatment response. A significant decrease in the M-spike or an improvement in the FLC ratio indicates a successful response. Conversely, a rise in these protein levels suggests disease progression or a relapse, requiring a therapy change.