Multiple myeloma is a rare cancer that occurs in bone marrow (soft tissue inside bones) in white blood cells called plasma cells that usually produce antibodies (immunoglobulins) which help the body to fight infection. However, in multiple myeloma the plasma cells become cancerous, producing a protein known by several names, including monoclonal immunoglobulin, monoclonal protein (M-protein), M-spike, or paraprotein.
The cancerous plasma cells fill up the bone marrow, eventually spreading to the outside of the bones and weakening them, causing bone fractures. The cancerous plasma cells additionally begin producing high levels of an antibody (immunoglobulin) that increases the viscosity (thickness) of the blood, leading to clotting, which can further cause kidney damage. While levels of one antibody increase, others drop, increasing the risk of infections. Red blood cell counts also drop, causing anemia, while blood calcium levels increase, leading to dehydration, constipation, and confusion.
Types of multiple myeloma include smoldering myeloma, which usually occurs without symptoms, and plasmacytoma, which is marked by abnormal plasma cells that occur in only one bone, causing pain.
Multiple myeloma mainly occurs in older people over the age of 60, males, African Americans, people who are obese, and those with a family history of multiple myeloma, or who have been diagnosed with a condition known as monoclonal gammopathy of uncertain significance (MGUS; see more about this condition below.)