What Is Multiple Myeloma?

Multiple myeloma is cancer that begins in plasma cells, a type of white blood cell. To understand multiple myeloma, it is helpful to know about normal blood cells.

Normal Blood Cells

Most blood cells develop from cells in the bone marrow called stem cells. Bone marrow is the soft material in the center of most bones.

Stem cells mature into different types of blood cells. Each type has a special function:

• White blood cells help fight infection. There are several types of white blood cells.
• Red blood cells carry oxygen to tissues throughout the body.
• Platelets help form blood clots that control bleeding.

Plasma cells are white blood cells that make antibodies. Antibodies are part of the immune system. They work with other parts of the immune system to help protect the body from germs and other harmful substances. Each type of plasma cell makes a different antibody.

Normal plasma cells help protect the body from germs and other harmful substances.

Myeloma Cells

Myeloma, like other cancers, begins in cells. Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, they die, and new cells take their place. In cancer, this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor.

Myeloma begins when a plasma cell becomes abnormal. The abnormal cell divides to make copies of itself. The new cells divide again and again, making more and more abnormal cells. The abnormal plasma cells are myeloma cells. Myeloma cells make antibodies called M proteins.

In time, myeloma cells collect in the bone marrow. They may crowd out normal blood cells. Myeloma cells also collect in the solid part of the bone. The disease is called "multiple myeloma" because it affects many bones. (If myeloma cells collect in only one bone, the single mass is called a plasmacytoma.)

Multiple myeloma is the most common type of plasma cell tumor. This booklet does not deal with other kinds of plasma cell tumors. The Cancer Information Service (1-800-4-CANCER) can send information about those diseases.

Myeloma cell (abnormal plasma cell) making M proteins.

No one knows the exact causes of multiple myeloma. Doctors can seldom explain why one person develops this disease and another does not. However, we do know that multiple myeloma is not contagious. You cannot "catch" it from another person.

Research has shown that people with certain risk factors are more likely than others to develop multiple myeloma. A risk factor is something that may increase the chance of developing a disease.

Studies have found the following risk factors for multiple myeloma:

• Age: Growing older increases the chance of developing multiple myeloma. Most people with myeloma are diagnosed after age 65. This disease is rare in people younger than 40.
• Race: The risk of multiple myeloma is highest among African Americans and lowest among Asian Americans. The reason for the difference between racial groups is not known.
• Personal history of monoclonal gammopathy of undetermined significance (MGUS): MGUS is a condition in which abnormal plasma cells make a low level of M proteins. MGUS is a benign condition, but it increases the risk of certain cancers, including multiple myeloma.

Scientists are studying other possible risk factors for multiple myeloma. Radiation, pesticides, hair dye, certain viruses, obesity, and diet are under study. But it is not clear that these factors are involved in the development of the disease. Researchers also are studying families in which more than one person has multiple myeloma. However, such families are extremely rare.

Most people who have known risk factors (being older, being African American, or having MGUS) do not get multiple myeloma. On the other hand, most people who do get the disease have no known risk factors. If you think you may be at risk, you should discuss this concern with your doctor.