What is multiple myeloma?

Multiple myeloma is a cancer that starts in plasma cells. Plasma cells are a type of white blood cell that makes antibodies (also called immunoglobulins) to help the body fight infection.

Plasma cells are found mainly in the bone marrow but are also in some other tissues and organs. Bone marrow is the soft, spongy tissue inside most bones where different types of blood cells are made. Plasma cells in the bone marrow sometimes change and no longer grow or behave normally. These abnormal plasma cells begin to divide uncontrollably and make more abnormal plasma cells. These changes can lead to multiple myeloma (a cancer of the plasma cells) or a precancerous condition called monoclonal gammopathy of undetermined significance (MGUS). Precancerous means that the cells are not yet cancer but there is a higher chance these abnormal changes will become cancer. In some cases, MGUS can develop into multiple myeloma.

Multiple myeloma develops when there is a buildup of many abnormal plasma cells (called myeloma cells) in the bone marrow. This makes it hard for other blood cells in the bone marrow to develop and work normally. This can cause anemia and fatigue because there are fewer red blood cells. The buildup of myeloma cells can also upset the balance of certain minerals in the body. The myeloma cells make a substance that leads to bone damage and high levels of calcium in the blood. Myeloma cells also make abnormal proteins that can affect other organs such as the kidneys.

Myeloma cells can form tumours in bones (called plasmacytomas). If there is only one tumour in a bone, it is called a solitary plasmacytoma. When many plasmacytomas are found in the bones, the condition is called multiple myeloma. Plasmacytomas can also form outside of the bones. These tumours are called extramedullary plasmacytomas.