Light micrograph section through human tissue showing multiple myeloma of the jaw. Multiple myeloma is a cancer that forms in a type of white blood cell called a plasma cell. Healthy plasma cells help fight infections by making antibodies that recognise and attack germs. In multiple myeloma, cancerous plasma cells accumulate in the bone marrow and crowd out healthy blood cells. Sometimes the disease primarily involves jaw bone or occurs along with other bones causing changes in oral cavity, which can be detected by a dentist.