Multiple myeloma is a type of cancer that begins in the body’s blood cells. It occurs when the bone marrow, the soft spongy material inside the bones, begins producing abnormal plasma cells. These abnormal plasma cells are called myeloma cells.
Myeloma cells can collect in the bone marrow and the outer layer of the bone, damaging the healthy tissue. However, multiple myeloma is not bone cancer. Although multiple myeloma affects the bones, it begins in blood cells, not bone cells. Bone cancer is a different disease.
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Over time, myeloma cells can spread and cause damage to bones throughout the body. Because this cancer usually affects many bones, it is referred to as “multiple myeloma.” If myeloma cells collect on only one bone, or on soft tissue at one place in the body, the single mass is called a solitary plasmacytoma. Abnormal growth of plasma cells can also interfere with the growth of normal red blood cells, white blood cells, and platelets. As a result, a person with multiple myeloma may be more susceptible to infection, anemia, and bleeding problems. Damage to the kidneys is also common.
Multiple myeloma primarily strikes people older than age 40. The disease is slightly more common in men than women, and it’s also more common among African Americans than among whites.
An estimated 19,920 new cases of multiple myeloma will be diagnosed in the United States in 2008, according to the American Cancer Society. Although there is not yet a definite cure for multiple myeloma, there are treatments that can keep the disease under control, often for years at a time.
How Multiple Myeloma Starts
Like other cancers, myeloma starts in the body’s cells. Scientists know that cancer occurs as a result of mutations, or abnormal changes, in the genes responsible for the regulation and health of cells. Genes are part of our DNA, which carry instructions for nearly everything our cells do.
Normally, the cells in our bodies replace themselves through an orderly process of cell growth: healthy new cells take over as old ones die out. But over time, mutations can make a healthy cell abnormal. That cell keeps dividing without control or order, producing more cells just like it. Doctors are not always sure how or why the genetic damage occurs. It likely results from a combination of factors, such as heredity (characteristics passed down through families) and environment (diet, lifestyle, exposure to chemicals and other substances, etc.).
Multiple myeloma is a type of cancer that begins in the body’s white blood cells. All of your blood cells first start out as stem cells in the bone marrow, the soft spongy material inside bones that functions as a blood cell “factory.” The stem cells can develop into three different types of blood cells: platelets, red blood cells, or white blood cells. Platelets are the blood cells responsible for clotting, or thickening, the blood and slowing its flow. Red blood cells carry oxygen and other needed substances to the tissues throughout the body. White blood cells defend the body against viruses, bacteria, and other foreign substances that can cause illness and disease.
Multiple myeloma starts in the white blood cells called lymphocytes. These are small white blood cells that play a key role in setting your body’s self-defense mechanism into action. A class of lymphocytes called B cells turn into plasma cells when any kind of foreign substance enters your body. These plasma cells produce the proteins called immunoglobulins, or antibodies, which defend your body against that specific substance. The body develops many types of plasma cells and can therefore protect itself against many types of invaders.
Multiple myeloma starts when a B cell turns into an abnormal plasma cell that keeps dividing without control or order. These fast-growing cells are called myeloma cells, and they are cancerous. They produce abnormal immunoglobulins, better known as M proteins, which can be measured in blood and sometimes in urine.
Types of Multiple Myeloma
Your particular type of multiple myeloma depends on what type of immunoglobulin (Ig, a protein also known as an antibody) is being overproduced by your cancerous plasma cells. These abnormal proteins are often referred to as M proteins, and they can be measured in the blood or urine.
The most common types of myeloma are IgG, which accounts for roughly 60 percent to 70 percent of all cases, and IgA, which accounts for about 20 percent. Other less common types include:
- IgM
- IgE
- IgD
- Kappa (k)
- Lamba (l).
To understand these types, it helps to learn more about immunoglobulins, the proteins that plasma cells produce to defend the body against threatening substances.
Immunoglobulins are made up of chains of proteins linked together. The two longer chains are called heavy chains, while the two shorter chains are called light chains. There are five different types of heavy chains, each with a different function in the body, that are used to classify immunoglobulins into five main categories: gamma, alpha, mu, epsilon, and delta.
Light chains are classified into one of two categories: kappa or lambda.
In most cases, the myeloma cells overproduce M proteins, detected in the blood, that fall into one of the five main categories. In some cases, however, the plasma cells produce only the light chain portion of the M protein (kappa or lambda). These light chains are measured in the urine, rather than in the blood. They are sometimes called Bence Jones proteins, named after the chemist who first discovered them. This type of myeloma is called light chain or Bence Jones myeloma, and it is responsible for about 15 percent to 20 percent of cases. Bence Jones proteins can clog the kidneys, damaging them and sometimes causing kidney failure.
Finally, a small number of people with multiple myeloma—about 1 percent—have a type called nonsecretory multiple myeloma. In these cases, the plasma cells do not produce M protein or light chains.