Multiple myeloma, or just myeloma, is cancer of plasma cells, a type of white blood cell found in the spongy tissue inside your bones, called bone marrow. Plasma cells make special proteins called antibodies that help your body fight germs.
Myeloma happens when plasma cells start to change and grow out of control. This means your body can’t make as many “normal” plasma cells as it should, which weakens your immune system. You might also have anemia due to fewer red blood cells or more bleeding than normal from cuts to the skin.
Inside your bones, red marrow helps make red blood cells, platelets, and white blood cells, including plasma cells. There are about 5.7 pounds of it inside the bones of an average adult.
Yellow marrow helps your body make fat, bone, and cartilage, and it can turn to red marrow in emergencies.
Multiple myeloma causes specific changes to cells in the bone marrow and the types of antibodies they make:
- Healthy plasma cells: These cells make antibodies that help fight bacteria and viruses.
- Healthy antibodies: Any number of intruders -- the common cold, the flu, or something more serious -- can trigger your plasma cells to make these antibodies to fight off illness.
- Myeloma plasma cells: These have a distinctive pale area that you can see under a microscope. Myeloma can crowd out healthy plasma cells, which makes your immune system weaker.
- Abnormal antibodies (M protein): This is what myeloma cells make instead of healthy antibodies. This M, or “monoclonal,” protein doesn’t fight germs. As it builds up in your blood and urine, it may cause kidney damage, tumors, bone damage, and a weakened immune system. Doctors sometimes find a small amount of M protein in a healthy person, something called monoclonal gammopathy of undetermined significance (MGUS).