Myeloma is a form of blood cancer caused by the excessive production of abnormal plasma cells in the bone marrow, the spongy tissue inside some bones where blood cells are generated.
Plasma cells typically play an important role in protecting the body against infections by producing antibodies, but these abnormal cells grow out of control and produce an abnormal antibody instead, called M protein, which can cause multiple complications.
Myeloma can be divided into different types, including inactive and active forms of the disease.
Monoclonal gammopathy of undetermined significance
Monoclonal gammopathy of undetermined significance (MGUS) is a benign, nonactive form of myeloma that is diagnosed when the M protein is detected in the blood. While this means that myeloma cells are present in the bone marrow, they do not form an actual tumor or mass and typically do not cause any symptoms.
Up to 5% of people aged 70 or older are eventually diagnosed with the condition.
Due to its benign nature, MGUS does not usually need treatment unless the M protein causes problems, such as nerve damage, bleedings, or heart or kidney problems. Given that there is 1% chance per year that the condition will progress to active myeloma, patients should be screened regularly (every six to 12 months) to check for a further increase in M protein levels or evidence of organ damage typically seen in active myeloma.
Smoldering multiple myeloma
Smoldering multiple myeloma (SMM) is an intermediate form between MGUS and active myeloma. People with SMM have higher M protein levels and/or more myeloma cells in the bone marrow (10–60% of all cells) than MGUS, but still do not experience any symptoms. Patients may also have small fragments of the M protein in the urine, in which case it is called Bence Jones protein.
Many, but not all, people with SMM progress to active myeloma. About 10% of SMM patients develop active myeloma each year in the first five years after diagnosis. Between five and 10 years after diagnosis, the risk drops to about 3% per year and is roughly 1% in following years.
Some people may have very slow disease that never becomes active myeloma, while high-risk SMM is likely to progress within a two-year period. In this later group, treatment before symptoms may slow the progression to active cancer.
A solitary plasmacytoma is a very rare plasma cell condition characterized by a localized, single tumor made of myeloma cells. The tumor is usually found in a bone (mainly those of the spine), but can also develop in soft tissue, such as that in the neck region or in lung and other organs. When the tumor is found outside the bone, it is called solitary extramedullary plasmacytoma.
People with solitary plasmacytoma do not have the typical symptoms of myeloma, but can have high levels of M protein. Comprehensive imaging analysis and lab work should be done to confirm the absence of multiple tumors or lesions, which characterizes multiple myeloma.
While radiation therapy is usually effective at eliminating the tumor, solitary plasmacytoma of the bone eventually progresses to myeloma in 70% of cases. As such, patients should be monitored closely with regular checkups following treatment.
Multiple myeloma occurs when there are multiple plasma cell tumors inside or outside bone. Symptoms of myeloma can be diverse and may not be obvious, especially in the disease’s early stages.
A myeloma diagnosis is based on the biopsy-proven presence of myeloma masses or at least 10% of plasma cells in the bone marrow, in addition to at least one other common symptom. These include abnormally low levels of red blood cells (anemia), high levels of calcium in the blood, blood lesions, kidney problems, and excessive levels of an immunoglobulin fragment, called light chain, which are suggestive of the presence of M protein.
Light Chain Myeloma
In about 20% of myeloma cases, the abnormal molecule produced by myeloma cells is not the full M protein but a smaller fragment of this antibody, called light chain. This condition is called light chain myeloma, also known as Bence Jones myeloma. These fragments can damage the kidneys.
In nonsecretory myeloma, which accounts for 3% of cases, the myeloma cells produce little or no M protein, meaning that neither that protein nor its light chain are detected in these patients. Bone marrow tests and imaging scans can help diagnose and monitor this type of myeloma.
Last updated: Dec. 21, 2021
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