Plasma cells are a type of white blood cell. They make antibodies that help us to fight infection.

Cancer occurs when normal body cells get out of control, multiply and spread. With myeloma, the cancer cells gradually grow and replace the healthy bone marrow. This makes the body less able to fight infection. The cancer cells also produce a substance that can weaken bones. Sometimes the cells collect in one place and form a lump (a tumour called a plasmacytoma), although this is not very common.