Myeloma, or multiple myeloma, is cancer of a certain type of white blood cell called a plasma cell, which is part of your immune system. Myeloma begins in the bone marrow, where blood cells are made.
What Happens in Healthy Bone Marrow
Bone marrow is found in the soft, spongy center of certain bones. Myeloma can affect any bones where marrow is active. Usually in adults marrow is active only in the skull, shoulders, spine, ribs, pelvis, and hips. (It’s not active lower in the arms, hands, legs or feet.)
Healthy bone marrow produces the three major types of blood cells our bodies need.
- White blood cells fight infection.
- Red blood cells carry oxygen.
- Platelets make the blood clot and stop bleeding.
Normally when bacteria or viruses enter your body, white blood cells called B lymphocytes, or B cells, turn into plasma cells. Then these plasma cells make antibodies to destroy the specific type of microorganism that entered your body. Antibodies, also called immunoglobulins, are complex proteins.
What Happens in Myeloma
In myeloma, plasma cells don’t reproduce normally. Instead, they become cancerous, and they divide and grow out of control. The cancerous plasma cells, also called myeloma cells, build up in the marrow and crowd out other healthy blood cells. This can increase your risk of infection (due to low white blood cells), anemia (due to low red blood cells) and blood-clotting problems (due to low platelets).
Also, myeloma cells don’t make effective antibodies. So people with myeloma have lower immune function than normal.
Instead of making effective antibodies, myeloma cells produce and release an abnormal protein, called M protein (M stands for monoclonal), and other chemicals. These substances can damage the immediate area, and they can travel through the bloodstream and damage other parts of the body.
For instance, some of the chemicals interact with bone cells, causing the hard, structural areas of bone to dissolve. These damaged areas are called osteolytic lesions. Lesions weaken the bone and can lead to fractures. Typically, bone damage is one of the main effects of myeloma. When bone dissolves, calcium is released into the bloodstream. A high level of calcium in the blood (hypercalcemia) can cause health problems, such as confusion and dehydration, and it can damage the kidneys.
M protein can also cause kidney damage, such as by damaging the small tubes inside these organs, and cause circulation problems because these proteins tend to stick to each other and to other tissues (like blood cells), which can thicken the blood.
Why it’s Called “Multiple” Myeloma
Most people with myeloma have myeloma tumors in several places in their body. That’s why this disease is often called “multiple myeloma.”
Some people with myeloma have only a single tumor. A single myeloma tumor is called a plasmacytoma. “Plasma-” refers to the type of cell affected. “-Cyte” is a general term for cell. “-Oma” means tumor. A plasmacytoma can form in a bone (called intramedullary disease) or in soft tissue outside the bone (called extramedullary disease). People with a single plasmacytoma in a bone often develop multiple myeloma later on.
Even though myeloma commonly affects the bones, it’s not a form of bone cancer. Myeloma begins in bone marrow cells, so it is a hematologic malignancy. The bone marrow cells give rise to all the mature blood cell types.