Multiple myeloma is a cancer that arises from a type of white blood cells called plasma cells. Plasma cells originate in the bone marrow and play an important role in the immune system.
Multiple myeloma develops when a normal plasma cell changes into myeloma cell — a cancerous cell that can multiply uncontrollably and produce identical copies of itself. This change occurs because of genetic mutations, or changes in a cell’s DNA.
People with multiple myeloma develop tumors in more than one location in the bone marrow — and sometimes outside the bone marrow — which is why the disease is called “multiple” myeloma.
As myeloma cells take over space in the bones where bone marrow grows, they prevent the marrow from producing essential blood cells, including red (oxygen-carrying) blood cells and other white (infection-fighting) blood cells.
Multiple myeloma is grouped into two main categories: asymptomatic (inactive) myeloma — also sometimes called smoldering myeloma — and symptomatic (active) myeloma. Asymptomatic myeloma is usually closely monitored but not treated until there are symptoms indicating that the disease has progressed. If the disease shows signs of being symptomatic, treatment is required.
The Role of Plasma Cells
Plasma cells specialize in the production of antibodies, proteins that identify and fight foreign invaders. Normally when you develop an infection, your plasma cells produce antibodies called immunoglobulins that help destroy infectious agents. Each immunoglobulin has a slightly different function in the body.
Though myeloma cells also produce immunoglobulins, they make them in excessive, sometimes harmful, amounts.
The excess immunoglobulins may be excreted in the urine. Therefore, most patients with myeloma have immunoglobulin protein, called Bence-Jones protein, in their urine. This can sometimes be damaging to the kidney.
Three percent of myeloma patients have a form of the disease called nonsecretory myeloma in which the cancerous plasma cells do not produce any immunoglobulin protein. In these patients, there is no protein in the blood or urine, but malignant plasma cells are present in the bone marrow.