Multiple myeloma

[Jason Yan]

Multiple myeloma is a cancer of plasma cells in which abnormal plasma cells multiply uncontrollably in the bone marrow and occasionally in other parts of the body.

People often have bone pain and fractures, and they may also have kidney problems, a weakened immune system (immunocompromise), weakness, and confusion.
Diagnosis is made by measuring the amounts of different types of antibodies in blood and urine and confirmed by a bone marrow biopsy.
Treatment often includes some combination of conventional chemotherapy drugs, corticosteroids, and one or more of the following: proteasome inhibitors (such as bortezomib , carfilzomib , or ixazomib ), immunomodulatory drugs (such as lenalidomide , thalidomide , or pomalidomide ), a nuclear export inhibitor selinexor , or monoclonal antibodies (including daratumumab or elotuzumab ).

Plasma cells develop from B cells (B lymphocytes), a type of white blood cell that normally produces antibodies (immunoglobulins). Antibodies are proteins that help the body fight infection. If a single plasma cell multiplies excessively, the resulting group of genetically identical cells (called a clone) produces a large quantity of a single type of antibody. Because this antibody is made by a single clone, it is called a monoclonal antibody and also is known as the M-protein.(See also Overview of Plasma Cell Disorders.)
The average age of people with multiple myeloma is about 65. Although its cause is not certain, the increased occurrence of multiple myeloma among close relatives indicates that heredity plays a role. Exposure to radiation is thought to be a possible cause, as is exposure to benzene and other solvents.
Normally, plasma cells make up less than 1% of the cells in the bone marrow. In multiple myeloma, typically the majority of bone marrow elements are cancerous plasma cells. The overabundance of these cancerous plasma cells in the bone marrow leads to the increased production of proteins that suppress the development of other normal bone marrow elements, including white blood cells, red blood cells, and platelets (cell-like particles that help the body form blood clots). In addition to producing a large amount of monoclonal antibody, the production of normal, defensive antibodies is markedly reduced.
Often, collections of cancerous plasma cells develop into tumors within bones. The cancerous cells also secrete substances that cause loss of bone, most commonly in the pelvic bones, spine, ribs, and skull. Infrequently, these tumors develop in areas other than bone, particularly in the lungs, liver, and kidneys.