Multiple myeloma is a type of cancer that occurs when plasma cells in the body start to overgrow in the bone marrow. Plasma cells are a type of white blood cell. Normally, as part of the immune system, plasma cells produce antibodies that help fight against disease and keep us healthy. In multiple myeloma, these plasma cells produce antibodies that are ineffective.
Multiple myeloma occurs when the overgrowth of plasma cells takes place in multiple areas of the bone marrow. Bone marrow is the soft spongy tissue in the middle part of the bone where blood cells are formed.
Most people diagnosed with multiple myeloma are over 65 years old. For 2010 the American Cancer Society estimates about 20,180 new cases of multiple myeloma in the United States and about 10,650 deaths. There is a 1 in 159 lifetime chance of developing multiple myeloma in the US.
It is not known what causes myeloma. Normally, only 5% or less of the bone marrow is made up of plasma cells. When a plasma cell becomes abnormal and begins multiplying, the cells are then called myeloma cells. Myeloma cells have special "adhesion molecules" that help them target bone marrow. In cases of myeloma, the plasma cells usually make up 10% or more of the bone marrow. Myeloma cells make a special type of protein to stimulate new blood vessels to form. These blood vessels provide oxygen and nutrients to the cancer cells.
Some risk factors for developing multiple myeloma include:
- a family history of multiple myeloma
- being male
- being older than 60 years of age
- people of African descent
- people with monoclonal gammopathy of undetermined significance (MGUS) - a precancerous disease of the plasma cell
There are other possible risk factors, such as obesity or exposure to high dose radiation and chemicals, but these have not been proven.