Multiple Myeloma

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What is Multiple Myeloma?

Multiple myeloma is a cancer of plasma cells in the bone marrow.

Normally, plasma cells form part of the immune system. They produce immunoglobulins (antibodies) which help fight infection. In multiple myeloma, abnormal plasma cells in the bone marrow multiply too fast. They take up too much space in the bone marrow and prevent the normal production of other blood cells, such as red and white blood cells. The plasma cells of multiple myeloma also produce large quantities of abnormal immunoglobulins, which cannot fight infection and which can cause damage to the kidneys.

The type of abnormal protein (called paraprotein) produced may be of any of the immunoglobulin types. (Immunoglobulins are specifically shaped antibodies made of protein.) The commonest are IgG (50%) and IgA (20%) with 20% also being of the "light chain" (part of the antibody) type. The rest are made up of a mixture of IgM, IgD and IgE myeloma while only 1 in 10 000 are non-secretory (i.e. has malignant cells in the bone marrow which do not produce any protein).

Who gets Multiple Myeloma?

Worldwide, the incidence of multiple myeloma is approximately 4 cases per every 100,000 people. In Australia, approximately 1200 new patients are diagnosed with multiple myeloma every year.

Multiple myeloma affects men more commonly than women. It is generally a disease of the elderly, with most patients being diagnosed at around 60 years of age. Multiple myeloma is rare before the age of 40.

Multiple myeloma is found more commonly in black African populations, and only rarely in Asian populations.

Predisposing Factors

There are a number of associations with multiple myeloma. Most of these are observed, rather than explained.

Occupations which may be associated with a higher risk of multiple myeloma include:

Farming
Woodworking
Leather working
Any occupation involving exposure to petroleum products.

In addition, exposure to high levels of ionising radiation may predispose to the development of multiple myeloma.

One factor which has been associated with a definite increase in risk of multiple myeloma is the presence of monoclonal gammopathy of undetermined significance (MGUS) in the blood. This is a condition which is seen in approximately 3-5% of people over 80 years of age. It is normally benign (not cancerous), but the presence of MGUS carries an annual 1-1.5% risk of developing active myeloma.

Progression

There are three major features of multiple myeloma:

Bone destruction: the expansion of the abnormal plasma cells in the bone marrow causes destruction of normal bone. This causes bone pain, and may lead to fractures where the bone has been weakened.
Bone marrow infiltration: the bone marrow is infiltrated by plasma cells. This means that normal blood cells cannot be produced, leading to low levels of red blood cells (anaemia), white blood cells (neutropaenia) and platelets (thrombocytopenia). Patients with multiple myeloma are at increased risk of developing infections, partly due to their impaired white cell production.
Kidney impairment: the kidneys may be damaged in multiple myeloma in a number of ways. Bone destruction by plasma cells leads to increased levels of calcium in the blood (hypercalcemia), which is harmful to the kidneys. In addition, the abnormal immunoglobulins produced by the plasma cells can be deposited in the kidney tubules and cause damage. Overall, kidney failure occurs in approximately one quarter of multiple myeloma patients.

Tumour spread in multiple myeloma is usually confined to the bones and bone marrow only. Rarely, the tumour may spread to the spleen, lymph nodes, or other organs.

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