Multiple myeloma is a type of blood cancer that develops in plasma cells, a form of white blood cell found in the bone marrow. The disease causes the accumulation of abnormal plasma cells, which produce faulty antibodies and impair the immune system. It can lead to bone fractures, anemia, kidney damage, and other complications. Treatment options include chemotherapy, targeted therapy, immunotherapy, and stem cell transplantation, with ongoing research focused on improving patient outcomes.