Myeloma is really not just one disease. There are several subtypes of myeloma since in different people, with the cancerous plasma cells making different antibodies. Doctors more often call these antibodies ‘immunoglobulins’. In each case of myeloma, only one type of immunoglobulin is overproduced, but this varies from patient to patient. There are 5 basic immunoglobulins – A, G, M, D and E. In myeloma, IgG is the most common, and IgE is the rarest. Immunoglobulins can be defined by the type of heavy chain they contain (A, G, M, D or E type). About 60 percent of all cases of myeloma involve the overproduction of IgG.
This section will describe the different types of myeloma.
MGUS can be a precursor of myeloma. In someone with MGUS:
Why is MGUS important? It is important because about 1 percent per year of people with MGUS will go on to develop myeloma or some other serious disorder. Currently, there is no clear way to predict who will progress to active myeloma. MGUS is usually monitored but not treated.
In some patients, there is a transitional state, called asymptomatic myeloma, that lies between MGUS and active myeloma. In asymptomatic myeloma there are few signs of active disease or the myeloma remains unchanged or stable.
Unlike MGUS, plasma cells may make up ten percent or more of the bone marrow and/or there is an M protein (M-spike or M-peak) greater than 30 g/L. However, there is still no anemia, renal failure, hypercalcemia or bone lesions. Because the disease is not yet active, SMM is usually observed but not treated. Supportive care, such as drugs to strengthen the bone, may be given.
Active myeloma is characterized by the presence of M proteins in the blood or urine and an increased number of plasma cells in the bone marrow. Another possible sign of active myeloma is the growth of a plasmacytoma or tumour in the bone or soft tissue.
People with symptomatic or active myeloma can develop complications such as anemia, kidney failure, or excessive levels of calcium (hypercalcemia) in the blood. Soft spots (lytic lesions) can appear on s of the bone. These lesions weaken the bone, causing pain and increasing the risk of fractures. People with symptomatic or active myeloma require treatment.
Myeloma is often referred to by the type of immunoglobulin (monoclonal protein) or light chain (kappa or lambda) that is over-produced by the cancerous plasma cells. The excessive level of one type of immunoglobulin is referred to as the M-protein, M-spike, M-peak or paraprotein.
In about 20 percent of cases, it is the IgA protein that is involved. Myeloma can also involve IgD or IgE but these forms occur less frequently.
Although a high level of M protein in the blood is a hallmark of myeloma, about 15 to 20 percent of patients produce only the light chain portion of the immunoglobulin. These are referred to as free light chains because they lack the heavy chain portion of the M protein. Light chain proteins are also referred to as Bence Jones proteins, after the physician and chemist who discovered them in the urine of myeloma patients.
When free light chain proteins are in the urine, they can accumulate in the kidney and damage it. They are not detected by routine urine testing, so specific tests are needed. Some laboratories now have tests that can detect and measure free light chains in the blood.
When very small amounts of M protein are produced by the malignant plasma cells this is called oligosecretory myeloma. Sensitive measurement of the M protein called Freelite® testing may be available in some centres and be of use in this type of myeloma.
There are some patients who may have both the M protein and the light chain myeloma.
About one percent of myeloma patients do not produce enough M proteins or light chains in the blood or urine to be detected. Again, Freelite® testing may help to measure levels of free light chains in these patients.
It is now known that there are multiple different genetic (DNA) abnormalities associated with myeloma. Having one of these genetic abnormalities affects how your disease will respond to different treatments. In the future, genetic profiling will play an increasingly important role in the customization of myeloma treatments.
Sometimes, myeloma is found in just one place in the body. This is called a solitary plasmacytoma. Sometimes, people with a solitary plasmacytoma will go on to develop myeloma later in life. Some doctors call this stage 1 myeloma.
Either single or multiple plasmacytomas can grow outside the bone marrow, for example in the head and neck area. Plasmacytoma that develops outside the bone marrow is called soft tissue plasmacytoma. It usually responds well to radiotherapy treatment.
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