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Types of Cancer > Myelomas > Overview
Multiple Myeloma: The Basics
Eric Shinohara, MD, MSCI
Affiliation:
Abramson Cancer Center of the University of Pennsylvania
Last Modified: February 23, 2008
What is a plasma cell?
Plasma cells are a mature type of B lymphocyte that usually make up less than 5% of the cells in the bone marrow. The bone marrow is a spongy material found primarily in the center of long bones. Bone marrow is comprised of a variety of cells, which gradually mature to form:
- Red blood cells (also known as erythrocytes), which carry inhaled oxygen from the lungs to other organs and carry carbon dioxide from the organs to the lungs to be exhaled.
- Platelets (also known as thrombocytes), which form clots.
- White blood cells (also known as leukocytes), which are comprised of granulocytes, lymphocytes, and monocytes, each of which has a different role in the immune system. Lymphocytes are made up of B and T lymphocytes. Plasma cells are a mature form of B-lymphocytes, which produce antibodies.
There are a large number of different pathogens, such as bacteria or viruses, which can attack your body. When your immune system fights an infection, it needs to make an antibody that specifically targets the pathogen causing that infection. Each plasma cell can only produce one specific kind of antibody. Individual plasma cells can then divide repeatedly to form copies of themselves, known as clones. This group of clonal plasma cells can produce large amounts of a single kind of antibody to fight the infection. There are several thousand different populations of plasma cell clones, which then allow the immune system to make a wide variety of antibodies to target the many different kinds of pathogens. Antibodies coat the pathogen that they are built to attack, and thus make it easier for other immune cells to also attack the pathogen. Cancer of the plasma cells is called multiple myeloma.
What is multiple myeloma?
Multiple myeloma is a disorder in which one population of clonal (identical) plasma cells starts to reproduce uncontrollably. These cells are known as malignant plasma cells, or myeloma cells. Myeloma cells produce large amounts of one type of antibody, which is known as the monoclonal protein or M-protein. As the myeloma cell population grows, it begins to overcrowd the bone marrow and prevents normal reproduction of the other blood cell types in the bone marrow. This also negatively affects the immune system because the bone marrow now predominantly produces only one type of antibody, and can no longer effectively target all pathogens. Thus there is increased risk of infection in patients with multiple myeloma. Anemia results when multiple myeloma prevents the bone marrow from producing enough red blood cells. As the plasma cells continue to multiply, they can invade and damage other organs. The monoclonal protein produced by plasma cells can also damage organs, specifically the kidneys. The acronym “CRAB” is often used to describe symptoms associate with organ damage by multiple myeloma: Hyper Calcemia (High levels of calcium in the blood, caused by bone lesions), Renal insufficiency (kidney failure), Anemia (Low red blood cell counts), and Bone lesions.
Am I at risk for multiple myeloma?
Approximately 14,600 people are diagnosed with multiple myeloma a year in the United States. Multiple myeloma comprises approximately 1% of all cancers and comprises about 10% of all “blood cancers”. The rate of multiple myeloma in African Americans is twice that seen in white Americans. Rates appear to be lower in Asians. This disease occurs slightly more commonly in men than in women, and the average age at diagnosis is 60 and people younger than 40 rarely develop this disease.
At this time, the cause of multiple myeloma is not well established. However, there appear to be several factors which increase the risk of developing multiple myeloma, such as extensive exposure to radiation, chemical resins, organic solvents, pesticides, and herbicides. There is also a herpes virus, Human Herpes Virus 8 (HHV-8), which is thought to be related to the development of multiple myeloma. People with first-degree relatives, such as a mother or brother, who have multiple myeloma, may also be at increased risk for developing the disease. However, a clear genetic mutation related to multiple myeloma has not been discovered.
People who have a condition known as Monoclonal Gammopathy of Unknown Significance (MGUS) are at increased risk for developing multiple myeloma. People with MGUS develop an increased population of clonal plasma cells, but not to the degree seen in multiple myeloma; these patients do not otherwise have symptoms associated with multiple myeloma. However, people with MGUS do have a 1-2% annual risk of developing multiple myeloma or a related malignant disease, such as leukemia or lymphoma. In light of this risk, when someone is first diagnosed with MGUS, it is recommended that blood tests be performed to check for elevated monoclonal protein levels every three months initially.