Causes
It is not known what causes myeloma. Normally, only 5% or less of the bone marrow is made up of plasma cells. When a plasma cell becomes abnormal and begins multiplying, the cells are then called myeloma cells. Myeloma cells have special "adhesion molecules" that help them target bone marrow. In cases of myeloma, the plasma cells usually make up 10% or more of the bone marrow. The myeloma cells interfere with the production of healthy cells in the bone marrow, causing reactions such as easily broken bones and an impaired immune system. Newly formed blood vessels are caused by the production of special proteins by the myeloma cells. These provide oxygen and nutrients to the new tumors.