Multiple myeloma, also known as plasma cell myeloma, is a cancer of plasma cells, a type of white blood cell normally responsible for producing antibodies. Initially, there are often no symptoms. When advanced, bone pain, bleeding, frequent infections, and anemia may occur. Complications may include amyloidosis. The cause is generally unknown. The underlying mechanism involves abnormal plasma cells producing abnormal antibodies which can cause kidney problems and overly thick blood. The plasma cells can also form a mass in the bone marrow or soft tissue. When there is only one mass it is known as a plasmacytoma and when there is more than one it is known as multiple myeloma. Multiple myeloma is diagnosed based on blood or urine tests finding abnormal antibodies, bone marrow biopsy finding cancerous plasma cells, and medical imaging finding bone lesions. Multiple myeloma is considered treatable but generally incurable. Remissions may be brought about with steroids, chemotherapy, thalidomide or lenalidomide, and stem cell transplant. Bisphosphonates and radiation therapy are sometimes used to reduce pain from bone lesions.