Multiple myeloma is a rare type of cancer. It starts with the uncontrolled production of plasma cells. These are a type of white blood cell in the bone marrow.
Healthy plasma cells make antibodies that help fight infection. But the myeloma plasma cells make abnormal antibodies. This can make it hard for your body to fight infection. And when there are too many plasma cells, they can crowd out normal blood cells. This can cause anemia and increased bruising or bleeding.
The plasma cells can collect in the bone to form small, painful tumors. These tumors can lead to broken bones. The plasma cells and the abnormal antibodies can also cause problems with the kidneys.