10 NCCN Guidelines for Patients ® : Multiple Myeloma, 2018 1 Multiple myeloma Multiple myeloma basics | M-proteins Multiple myeloma basics Multiple myeloma (also simply called myeloma) is a cancer that starts in plasma cells. Plasma cells grow and then divide to make new cells. New cells are made as the body needs them. When plasma cells grow old or get damaged, they die. Genes are the instructions in cells for making new cells and controlling how cells behave. Changes in genes turn plasma cells into myeloma cancer cells. An abnormal change in a gene is called a gene mutation or defect. In contrast to healthy plasma cells, myeloma cancer cells make more and more new cells that aren’t needed and don’t die quickly when old or damaged. See Figure 3. The myeloma cells continue to make millions of copies of themselves. As a result, a group of myeloma cells with the same gene mutation forms, often referred to as a clone of cells. Myeloma cells may be spread throughout the bone marrow or form masses growing in one or more spots outside of the bone marrow. These masses can destroy the bone around them as they grow. A mass of myeloma cells is called a plasmacytoma . When there is only one mass of myeloma cells, it is called a solitary plasmacytoma . When myeloma cells grow and spread throughout the bone marrow, it is called multiple myeloma . The myeloma cells can crowd out normal blood cells in the bone marrow, invade bone tissue, and spread all over the body. It is not fully known why a normal plasma cell changes into a myeloma cancer cell. M-proteins Like plasma cells, myeloma cells also make antibodies. But, the antibodies made by myeloma cells are all copies of one specific type of antibody. Since they are made by a clone of myeloma cells, they are called monoclonal proteins or M-proteins. Myeloma cells make M-proteins without control and not in response to a specific germ in the body. M-proteins don’t help to fight infections. In most patients, myeloma cells make very large amounts of M-proteins. Rarely, the myeloma cells make very little or no M-protein. This is called oligosecretory or nonsecretory myeloma. Normal antibodies are made of two heavy protein chains and two light protein chains. See Figure 4. Heavy chains are one of five types—A, D, G, E, or M. Light chains are one of two types—kappa or lambda. The form of heavy chain defines the type of antibody. Like normal antibodies, M-proteins are also made of two heavy chains and two light chains. However, myeloma cells tend to make more light chains than needed to form a complete M-protein. This leads to excess light chains that aren’t attached to a heavy chain. These are called free light chains. High levels of free light chains are found in the urine of most people with myeloma. The light chains from M-proteins found in the urine are also called Bence Jones proteins. In about 15 out of 100 people with myeloma, the myeloma cells only make light chains and no complete M-proteins. Doctors call this light chain myeloma or Bence Jones myeloma.