What is multiple myeloma?
Multiple myeloma is a cancer of the bone marrow. It develops when malignant plasma cells start increasing in the bone marrow, which is the spongy tissue found inside larger bones. Myeloma is sometimes also called plasma cell cancer.
Myeloma belongs to blood cancers and is the second most common of these after lymphoma. In Finland, myeloma and other plasma cell diseases are diagnosed in 320–420 new patients each year.
Myeloma occurs particularly in elderly people; the mean age at diagnosis is 65–70 years. Myeloma is rare in people under the age of 40 years. Men get myeloma a little more often than women.
What causes myeloma?
The cause of myeloma is not known, and it is not considered an inherited disease. At present it is not known how the development of myeloma can be prevented.
No major risk factors for multiple myeloma are known. Ethnic origin may have a minor role in morbidity. For an unknown reason, Black people have twice the risk of getting myeloma compared with Caucasians. Exposure to radiation, asbestos, benzene and pesticides may increase the risk.
Myeloma is almost always preceded by a condition called MGUS (monoclonal gammopathy of undetermined significance), which can be seen in blood or urine samples. This is an asymptomatic precancerous condition that may transform into true myeloma over the years. The possibility that an MGUS develops into myeloma is only about one per cent per year. The reason why MGUS transforms into myeloma is not yet known.
How does myeloma develop and progress?
Plasma cells are a type of white blood cells that produce antibodies to fight harmful bacteria and infections in the body. Thus plasma cells have an important role in the immune system.
In myeloma, normal plasma cells turn malignant via a process that has many phases. The malignant plasma cells produce an abnormal antibody called paraprotein (or M component) that lacks the ability to resist infections.
Myeloma starts to develop when the malignant plasma cells increase in an uncontrolled fashion:
- By increasing rapidly, myeloma cells take up space in the bone marrow and replace normal bone marrow cells.
- This then starts to interfere with the normal functioning of, and blood formation in, the bone marrow. The decrease in the number of red blood cells results in anaemia, and the lack of white blood cells predisposes to infections.
- Even though sick plasma cells are present particularly in the bone marrow, they often spread, forming cancerous lesions elsewhere in the skeleton and the body. These lesions are called plasmacytomas. The name of the disease, multiple myeloma, refers particularly to the fact that lesions are typically found in several locations in the body.
In healthy bone marrow, a type of white blood cells called B cells develop into plasma cells, which produce antibodies when harmful substances (antigens) enter the body. In myeloma, damage to the DNA of a B cell transforms the plasma cells into myeloma cells. The cancer cells increase, take up room from normal blood cells and start producing large amounts of paraprotein.
The prognosis for multiple myeloma generally depends on
- characteristics of the cancer and symptoms in patients
- disease classification to be defined at diagnosis.
Based on these, the physician decides when to start treating the myeloma and what are the best available treatment options
At present, multiple myeloma is incurable, but thanks to advanced treatments, those with the diagnosis can expect longer lives. Modern treatment also alleviates the symptoms of myeloma better and improves quality of life.