Multiple myeloma is a cancer that forms in a type of white blood cell called a plasma cell. Plasma cells help you fight infections by making antibodies that recognize and attack germs. Multiple myeloma causes cancer cells to accumulate in the bone marrow, where they crowd out healthy blood cells. Rather than produce helpful antibodies, the cancer cells produce abnormal proteins that can cause complications. Treatment for multiple myeloma isn’t always necessary for people who aren’t experiencing any signs or symptoms. For people with multiple myeloma who require treatment, a number of treatments are available to help control the disease.