Multiple myeloma is characterized by the excessive growth and malfunction of plasma cells in the bone marrow. The growth of these extra plasma cells interferes with the production of red blood cells, white blood cells, and platelets. This causes anemia, susceptibility to infection, and increased tendencies toward bleeding.

As the cancer cells grow and expand in the bone marrow, they also cause pain and destruction of the bones. If the bones in the spine are affected, compression of the nerves may result causing numbness or paralysis.

Renal failure (kidney failure) is a frequent complication caused by excess calcium in the blood that results from bone destruction. Multiple myeloma mainly affects older adults. Other risk factors are unknown. This disease is rare and only 3 new cases per 100,000 people per year occur.