Multiple myeloma, a cancer of the bone marrow, arises from plasma cells. Plasma cells are a type of fully developed B lymphocytes (B cells), a group of white blood cells that originate in the bone marrow and play an important role in the immune system. Plasma cells are specialized in the production of antibodies, Y-shaped proteins that identify and fight foreign invaders.
Normally, when you develop an infection B cells respond by rapidly maturing into plasma cells. These plasma cells produce antibodies called immunoglobulins — IgG, IgA, IgM, IgE, or IgD — that help destroy infectious agents. Each of these proteins has a slightly different function in the body.
Multiple myeloma develops when a normal plasma cell turns into a malignant (cancerous) cell, called a myeloma cell, and begins to multiply uncontrollably, producing identical copies of itself. This transformation results from genetic mutations — changes in a cell’s DNA, which can occur as plasma cells divide. People with this condition develop tumors in more than one location in the bone marrow — or sometimes outside the bone marrow — which is why the disease is called “multiple” myeloma.
As myeloma cells take over space in the bones where bone marrow grows, they prevent the marrow from producing essential blood cells, including red (oxygen-carrying) blood cells and other white (infection-fighting) blood cells. Though myeloma cells also produce immunoglobulins, they make them in excessive, sometimes harmful, amounts.
The excess immunoglobulins may be excreted in the urine. Therefore, most patients with myeloma have immunoglobulin protein, called Bence-Jones protein, in their urine, which can sometimes be damaging to the kidney. Three percent of myeloma patients have a form of the disease called nonsecretory myeloma in which the cancerous plasma cells do not produce any immunoglobulin protein. In these patients, there is no protein in the blood or urine, but malignant plasma cells are present in the bone marrow.
Multiple myeloma is grouped into two main categories: asymptomatic (inactive) myeloma – also sometimes called smoldering myeloma – and symptomatic (active) myeloma. Asymptomatic myeloma is usually closely monitored but not treated until there are symptoms indicating that the disease has progressed. If the disease shows signs of being symptomatic, treatment is required.
Multiple myeloma is more common in men than women, and more common in African Americans than in those of other backgrounds. The median age at the time of diagnosis is 63.
Most people with multiple myeloma do not have clearly identifiable risk factors. There is no reliable evidence that bacterial or viral infections cause myeloma. The disease rarely affects more than one person in a family, although immediate family members do a have a slightly increased risk of developing a similar condition.
However, there is some evidence that environmental exposure to certain kinds of chemicals can slightly increase risk of multiple myeloma, as there are slightly higher rates of disease in agricultural workers exposed to pesticides and fertilizers, petrochemical and sheet metal workers, and those exposed to wood dust or fuel oil products.
Over time, as myeloma cells divide and increase in number, they can affect the body in various ways. Symptoms can include:
- Bone pain and skeletal fractures, including compression fractures of the spine, which can cause severe pain, particularly in the back. A backache that lasts for months can be a signal that multiple myeloma is affecting bones in the spine and/or the ribs.
- Frequent infections, especially bacterial infections of the respiratory and urinary tracts, which occur because the immune system is weakened.
- Fatigue, weight loss, and general discomfort caused by anemia (insufficient red blood cells).
- Nausea, vomiting, altered mental state, depression, and headache, caused by abnormally high calcium levels in the blood (hypercalcemia).
- Loss of kidney function, leading to fatigue, buildup of fluid in the lower limbs, nausea, and vomiting.
- Bruising, rashes, nosebleeds, vision loss, headache, dizziness, and peripheral neuropathy (numbness, tingling, and burning pain in the extremities) caused by blood that has thickened (a condition called hyperviscosity) due to high levels of protein.
- Shooting pains in the arms and legs caused by a tumor in the spinal column pressing on nerves.
In about one-third of patients, multiple myeloma is detected before symptoms appear through routine blood tests that show elevated levels of immunoglobulin proteins.