What is multiple myeloma?
Multiple myeloma is a type of cancer formed by cancerous plasma cells. Normal plasma cells are found in the bone marrow and are an important part of the body’s immune system.
The immune system is made up of several types of cells that work together to fight infections. Lymph cells (called lymphocytes) are the main type of cell in the immune system. There are 2 main types of lymph cells: T cells and B cells.
When B cells respond to an infection, they change into plasma cells. The plasma cells are mainly in the bone marrow — the soft, inner part of some bones. The plasma cells make proteins called antibodies that attack and help kill germs.
When plasma cells grow out of control, they can form a tumor, usually in a bone. If there is only one plasma cell tumor, it is called an isolated (or solitary) plasmacytoma. When there is more than one plasma cell tumor, it is called multiple myeloma.
Having too many plasma cells can cause problems in the bone marrow, where all blood cells are made. The cancer cells crowd out the normal cells and the bone marrow may not be able to make enough red blood cells, platelets, or normal white blood cells. This can cause problems like:
- Anemia: A shortage of red blood cells, which can cause you to be pale, weak, and tired.
- Bruising or bleeding: Cells called platelets help stop bleeding. Without enough platelets, there can be a lot of bruising or bleeding.
- Leukopenia: A shortage of white blood cells, which can make it very hard for the body to fight infections.
Another problem is that the myeloma cells do not help protect the body from infections. Instead of making normal antibodies, they all make many copies of the same antibody. Because it only one antibody, it isn’t helpful in fighting germs.
The myeloma also reacts with cells that work to keep the bones strong. Normally, some cells build up bones and other cells work to dissolve them. Together, they give bone its proper shape and keep it healthy and strong. But myeloma cells cause too much bone to dissolve. Then the body does not get a signal to make new bone. Old bone is broken down without new bone to replace it. This makes the bones weak, and they break easily. When bone dissolves, it releases calcium into the blood. Often in myeloma the blood level of calcium gets too high. This causes problems like feeling very tired and weak. In extreme cases, it can even cause a person to go into a coma.
The myeloma protein can be toxic to the kidneys, leading to problems with kidney function or even kidney failure.
Having many copies of the same antibody is called a monoclonal gammopathy. This is seen in multiple myeloma and some other diseases, but it can also be present and not cause problems. This is called monoclonal gammopathy of undetermined significance or MGUS. There may be extra plasma cells in the bone marrow, but they do not form a tumor or cause any problems. They do not cause the bones to weaken. But with time, MGUS can turn into multiple myeloma or another disease. People with MGUS don’t need treatment, but they are watched closely to see if they get a disease that does need to be treated (like multiple myeloma).
Last Medical Review: 02/01/2013
Last Revised: 02/13/2013