Multiple myeloma is the most common plasma cell cancer. The bones and bone marrow are the main sites where myeloma cells (abnormal plasma cells) are produced. The myeloma cells form tumours (called plasmacytomas) in many bones in the body.
The buildup of myeloma cells causes:
- less normal blood cells in the bone marrow
- bones to become weakened or damaged
- There are 2 kinds of bone cells that work together to develop a bone into its proper shape:
- Osteoblasts make bone.
- Osteoclasts dissolve bone.
- Myeloma cells produce a substance that stimulates osteoclasts and speeds up the destruction of bone.
- complications, such as infection, bone pain and fractures
Smouldering or indolent multiple myeloma
Smouldering or indolent multiple myeloma is also called asymptomatic myeloma because it does not cause any symptoms. This type of myeloma is a condition between monoclonal gammopathy of undetermined significance (MGUS) and active (symptomatic) multiple myeloma. People with smouldering or indolent multiple myeloma have at least one of the following:
- Plasma cells make up 10% or more of the blood cells in the bone marrow.
- M-protein level in the blood is 30 g/L or more.
Smouldering or indolent multiple myeloma does not cause anemia, kidney failure, high blood calcium (hypercalcemia) or bone lesions. Most people with this type of multiple myeloma will develop active multiple myeloma. Smouldering or indolent multiple myeloma may be categorized as a stage I multiple myeloma if the features are the same.
Active multiple myeloma
People with active multiple myeloma have symptoms related to the disease and any of the following:
- M-proteins in the blood or urine
- increased number of plasma cells in the bone marrow (more than 10%)
- a tumour containing myeloma cells (plasmacytoma) in the bone or soft tissue
- evidence of anemia, kidney failure or high blood calcium (hypercalcemia)
- osteolytic lesions (weakened areas of bone)
Solitary plasmacytoma of the bone
A plasmacytoma develops when myeloma cells collect in one place and form a single tumour. Solitary plasmacytoma of the bone is one tumour made up of myeloma cells found in one bone (rather than multiple tumours in different locations, as in multiple myeloma). There are no other features of multiple myeloma. There are no osteolytic lesions on x-ray and the bone marrow is normal. The main symptom of a solitary plasmacytoma of the bone is pain at the site of tumour. About 50%–60% of people with solitary plasmacytoma will develop multiple myeloma.
Solitary plasmacytoma of the bone is sometimes considered a stage I myeloma.
Multiple solitary plasmacytomas
Multiple solitary plasmacytomas are separate plasmacytomas that occur in bones or soft tissues. All the plasmacytomas appear around the same time. There are no other features of multiple myeloma. There are no osteolytic lesions on x-ray and the bone marrow is normal.
The main treatment for multiple solitary plasmacytomas is radiation therapy. If there are large tumours or the tumours do not respond to radiation therapy, a stem cell transplant may be given.
Extramedullary plasmacytomas start outside the bone marrow (extramedullary) in soft tissues of the body. It is most common in areas of the upper respiratory tract, such as the throat, sinuses, back of the nose, nasal cavity and larynx (voice box). It may also occur in other areas, including the gastrointestinal tract, breast and brain. Symptoms vary depending on the location of the tumour in the body. Extramedullary plasmacytomas progress to multiple myeloma in 11%–30% of cases.
Diagnosis of extramedullary plasmacytoma is made after a biopsy of the tumour. The main treatment for extramedullary plasmacytoma is radiation therapy, surgery, or both.
Light chain myeloma
Some people with multiple myeloma have myeloma cells that do not produce a complete immunoglobulin. People with light chain myeloma only produce the light chain part of the immunoglobulin. They do not produce the heavy chain. Light chain proteins are also called Bence Jones proteins.
Light chain proteins can collect in and damage the kidneys. Light chains are smaller than M-proteins and show up better in the urine than the blood. This is because light chains are filtered out of the blood when they reach the kidneys. About 20% of people with multiple myeloma have light chain myeloma.
Some people with multiple myeloma have myeloma cells that do not release (secrete) enough M-proteins or light chains into the blood or urine to be detected by protein electrophoresis. Non-secretory myeloma is characterized by myeloma cells in the bone marrow. X-rays will often show osteolytic lesions in a person with non-secretory myeloma.
Rare types of multiple myeloma
The most common immunoglobulins (Ig) made by myeloma cells in multiple myeloma are IgG, IgA and IgM. Less commonly, IgD or IgE is involved.
- immunoglobulin D (IgD) myeloma
- About 2% of people with multiple myeloma have the IgD type.
- IgD multiple myeloma causes the same signs and symptoms as other types of multiple myeloma.
- IgD myeloma tends to affect people at a slightly younger age (around 55–60 years).
- immunoglobulin E (IgE) myeloma
- IgE is the rarest type of multiple myeloma.
- IgE multiple myeloma causes the same signs and symptoms as other types of multiple myeloma.