Multiple myeloma is a form of cancer affecting the plasma cells, a variety of white blood cell found in the bone marrow. It is a relatively rare cancer with an estimated 30,000 cases diagnosed each year in the United States, according to figures from the American Cancer Society. 

It is caused by the abnormal development of plasma cells in the bone marrow, which reproduce quickly and eventually outnumber the healthy cells in the bone marrow. There are two types of multiple myeloma: indolent myeloma, which has no noticeable symptoms; and solitary plasmacytoma, which causes a tumor to form, usually in the bone. 

Symptoms of multiple myeloma are few, particularly in the early stages of the disease, but when they start to appear they may include nausea, constipation, bone pain, loss of appetite, fatigue, increased susceptibility to infection, weight loss, weakness or numbness of the legs, excessive thirst, and confusion. It may also result in bone problems, reduced kidney function, and anemia.

Treatment of multiple myeloma may include surgery, radiation therapy, and medication. Drug classes commonly used to treat multiple myeloma include immunomodulators, angiogenesis inhibitors, other antineoplastic agents, injectable bisphosphonate bone calcium regulators, nitrogen mustard analogs, histone deacetylase inhibitors, colony-stimulating factors, protein kinase inhibitors, and anthracyclines.