Multiple myeloma is a blood cancer that starts with one or more changes to the DNA of a single stem cell in the bone marrow. Stem cells form blood cells (white cells, red cells and platelets).
Myeloma develops in a white blood cell called a B cell. Some B cells transform plasma cells, which make antibodies – these are the cells that fight a wide range of infections. In myeloma, an injury to a B cell’s DNA causes an abnormal change that can start the transformation of a normal plasma cell into a cancerous cell. Because cancerous cells multiply at a faster rate than normal cells and don’t die when they should, one antibody will grow out of control and eventually crowd out other plasma cells.
If not treated, the myeloma cells can:
Your immune system is made up of lymphocytes (T cells and B cells) that work together to fight infections and other diseases. When B cells respond to an infection, they mature and change into plasma cells. Plasma cells make the antibodies (also called immunoglobulins) that help the body attack and kill germs. Plasma cells are mainly found in the bone marrow. Bone marrow is the soft tissue inside some hollow bones. When plasma cells become cancerous and grow out of control, they can produce a tumor called a plasmacytoma. These tumors generally develop in a bone, but they are also rarely found in other tissues. If there is only a single plasma cell tumor, it is called an isolated (or solitary) plasmacytoma. When there is more than one plasma cell tumor, it is called multiple myeloma.
Source: Leukemia & Lymphoma Society, American Cancer Society