Myeloma is a cancer of the plasma cells in the bone marrow, the spongy tissue inside of bones. Myeloma begins when healthy plasma cells change and grow uncontrollably. Plasma cells are a part of the body's immune system and produce antibodies that help the body fight infection. Abnormal plasma cells can crowd out or suppress the growth of other cells in the bone marrow that produce red blood cells, white blood cells, and platelets. This suppression may result in anemia (from a shortage of red blood cells), excessive bleeding from cuts (from a shortage of platelets), and a decreased ability to fight infection (from a shortage of white blood cells and the body’s inability to respond to infection normally).
Like regular plasma cells, myeloma cells can produce antibodies. However, myeloma cells are unable to produce healthy, functioning antibodies. Instead, they make what is called “monoclonal protein,” or “M protein,” which can build up in the blood and urine, potentially causing damage to the kidneys and other organs. A healthy person who is found to have a small amount of this “M protein” is said to have monoclonal gammopathy of unknown significance (MGUS).
Myeloma often causes structural bone damage resulting in painful fractures or bone breaks. Myeloma is usually called multiple myeloma because most people (90%) have multiple bone lesions at the time it is diagnosed. Solitary plasmacytoma is a mass of myeloma cells that involve only one site in the bone or other organs, most commonly in the upper respiratory tract, including the nose and throat. Extramedullary plasmacytoma describes myeloma that started outside the bone marrow in locations such as the lymph glands, sinuses, throat, liver, or under the skin.
Normal Bone MarrowClick to Enlarge
Multiple Myeloma DiseaseClick to Enlarge
These images used with permission by the College of American Pathologists.
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