Multiple myeloma is a type of cancer that affects the plasma type of white blood cells. Myeloma cells tend to collect in the bone marrow and in the hard, outer part of bones. Sometimes they collect in only one bone and form a single mass, or tumor, called a plasmacytoma. In most cases, however, the myeloma cells collect in many bones, often forming many tumors and causing other problems. When this happens, the disease is called multiple myeloma.
Please note that cancer is classified by the type of cell, or the part of the body, in which the disease begins. Although plasmacytoma and multiple myeloma affect the bones, they begin in cells of the immune system. This type of cancer is different from bone cancer, which actually begins in cells that form the hard, outer part of the bone. You should know this because the diagnosis and treatment of plasmacytoma and multiple myeloma are different from the diagnosis and treatment of bone cancer.
