Multiple myeloma is a rare cancer of the bone marrow. It results from the abnormal growth of plasma cells in the bone marrow. Plasma cells normally produce antibodies. As these abnormal or malignant plasma cells multiply, they produce large quantities of abnormal antibodies. These abnormal antibodies collect in the blood and urine. As the plasma cell tumor grows, it also destroys the bone around it. These events lead to bone pain, kidney damage, and a weak immune system.

Cancer occurs when cells in the body (in this case plasma cells) divide without control or order. Normally, cells divide in a regulated manner. If cells keep dividing uncontrollably, a mass of tissue forms, called a growth or tumor. The term cancer refers to malignant tumors, which can invade nearby tissue and spread to other parts of the body. A benign tumor does not invade or spread.

Bone Marrow in Adult
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The cause of multiple myeloma is not known.