What is Multiple Myeloma?

Multiple myeloma is a type of cancer that affects the blood plasma cells. Blood cells such as red blood cells, white blood cells, and platelets are produced in the bone marrow, which is the soft, spongy interior of bones. Plasma cells are a type of white blood cell that produce specific proteins called antibodies to help the body fight disease and infection.

In multiple myeloma, malignant plasma cells multiply uncontrollably in the bone marrow. These myeloma cells can collect in the bones and soft tissues of the body, forming tumors called plasmacytomas, which can cause bone erosion. Myeloma cells can crowd out healthy blood cells in the bone marrow and interfere with normal blood cell production, leading to conditions such as anemia (low red blood cells), leukopenia (low white blood cells), and thrombocytopenia (low platelets). Myeloma cells can also interfere with the cells that keep bones strong and healthy, causing bone pain, weakened bones, and lytic lesions (soft spots on bones). Thus, people with multiple myeloma commonly have weak bones and an increased risk for fracture compared to healthy people. This bone damage may increase the level of calcium in the blood, leading to a condition known as hypercalcemia.

As myeloma cells multiply, they create many copies of the same abnormal antibody (called an M-protein or monoclonal antibody) as well as smaller proteins called light chains which can be detected in blood and/or urine. When they are detected in urine they can also be called Bence-Jones proteins. This excess of abnormal antibodies is known as a monoclonal gammopathy. These abnormal antibodies do not function correctly and accumulate in the blood and urine. The excess M-proteins and blood calcium can put extra stress on the kidneys, which filter waste and excess water from the blood and turn it into urine. This stress can damage the kidneys and cause additional complications, such as kidney failure and worsening hypercalcemia.

These malignant plasma cells can also suppress the function of normal plasma cells and prevent them from producing healthy antibodies. Monoclonal gammopathy of undetermined significance (MGUS) is a precursor condition in which a person has a small level of abnormal plasma cells in the bone marrow that produce a small level paraprotein or light chains in blood and/or urine but does not have multiple myeloma.  Because MGUS is a precursor condition to multiple myeloma, some patients may ultimately develop MM, whereas the majority of people will not.  Observation is recommended because only a small portion of patients will have transformation to active multiple myeloma.