What is it?Multiple myeloma is a cancer of the
plasma cells. Found in the bone marrow, plasma cells develop from
B lymphocytes. Their primary function is to produce antibodies – targeted immunoglobulin proteins that help protect the body against microscopic invaders. Normally, plasma cells are produced as needed and share space in the bone marrow with maturing red blood cells (RBCs - which carry oxygen), platelets (cell fragments that are used in the clotting process), and several types of white blood cells (WBCs - which are used by the body to fight infection). Sometimes, however, a plasma cell may become
malignant. It begins to divide uncontrollably, generating numerous malignant copies of itself (clones) that form tumors in the bone marrow. In time, these tumors interfere with normal cell production and erode the surrounding bone, producing soft spots and holes (lytic lesions). Since the malignant cells are clones, derived from a single plasma cell, they all produce the same antibody molecule, an abnormal monoclonal immunoglobulin (M-protein) that is released into the blood and, sometimes, excreted in the urine.
Normally, the body makes many different types of immunoglobulins (antibodies) that can attack many different types of bacteria and viruses. Normal immunoglobulins are composed of four parts, two identical heavy chains (of one of five different types) and two identical light chains (of one of two different types). With multiple myeloma, patients produce only one type of heavy chains and only only one type of light chains, or may produce an excess of only one of the chain types. Patients producing only light chains are in the minority; the M-proteins that they create are referred to as Bence Jones proteins, or free light chains. Bence Jones proteins are typically found in small quantities in the blood and large quantities in the urine.
Symptoms and Signs
Many patients with multiple myeloma show no symptoms for many years. Eventually, most patients develop some evidence of the disease related to weakened bones (bone pain), decreased numbers of red or white blood cells (anemia, infections), and kidney failure (increased creatinine). As bones weaken, soft spots and fractures may develop. Destruction of the bone frequently increases the level of calcium in the blood, leading to symptoms of hypercalcemia (loss of appetite, nausea, thirst, fatigue, constipation, and confusion). Decreases in the number of normal WBCs, RBCs, and platelets often result in recurrent infections, anemia, bleeding, and bruising. Bence Jones proteins (free light chains) can lodge in the kidneys and may permanently damage them. In some cases, an increase in the viscosity of the blood may lead to headaches.
Risks
Multiple myeloma is relatively uncommon. The American Cancer Society estimates that about 15,270 new cases of multiple myeloma will be diagnosed in the U.S. during 2004 and that about 11,070 people with multiple myeloma will die. The cause of multiple myeloma is not yet known. The risk of developing it increases with age, with the majority of cases being diagnosed in patients 60 years or older. While there are a few families who have a higher incidence of multiple myeloma, most patients will not have any affected relatives. It is thought that some cases may be associated with occupational exposure to toxins and/or solvents, such as benzene.
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