Myeloma is the second most common type of blood cancer. It affects plasma cells, a type of white blood cell that normally helps the body protect itself against infection.
Plasma cells have the ability to produce antibodies, special proteins that fight bacteria, viruses and other invaders that can harm the body.
Normally, B-lymphocytes mature into plasma cells. Sometimes, the B-lymphocytes fail to differentiate (or develop) properly into mature plasma cells and form myeloma cells instead. These immature, abnormal cells divide uncontrollably, and become malignant (cancerous). The overabundant myeloma cells begin to crowd out normal cells in the bone marrow, causing problems such as anemia (too few red blood cells), leukopenia (too few white blood cells) or thrombocytopenia (too few platelets that make blood clot).
In the disease called multiple myeloma, malignant plasma cells create multiple tumors (plasmacytomas) within bones and soft tissues. The accumulating plasma cells can lead to bone fractures and increased levels of calcium in the blood. They can also cause problems within organs, especially the kidneys.
Solitary plasmacytomas are another type of plasma cell cancer. Instead of multiple tumors, a single tumor can arise in any part of the body. Most people with a solitary plasmacytoma will eventually develop multiple myeloma, and will require close monitoring.
Myeloma cells also produce an immunoglobulin protein (antibody) called monoclonal (M) protein, or paraprotein. The presence of M protein is a hallmark of myeloma. Unlike a “good” immunoglobulin, M protein does not protect the body. Because levels of normal antibodies are often low in people with myeloma, they can develop frequent infections.
Related Plasma Cell Disorders
Waldenström’s macroglobulinemia is a related disorder in which abnormal plasma cells divide uncontrollably and produce a very large form of M protein. As levels of this protein increase, the blood can become thickened, and the lymph nodes, liver and spleen may become enlarged.
Sometimes before multiple myeloma develops, it is preceded by a condition called monoclonal gammopathy of undetermined significance (MGUS). This condition also involves a slight overgrowth of plasma cells. Although the cells produce excess antibody protein, they do not form a tumor, and do not cause symptoms or health problems. However, many people with MGUS eventually develop multiple myeloma, lymphoma or a disease called amyloidosis. People with MGUS do not require immediate treatment, but should be monitored regularly.