Overview of Multiple Myeloma
Multiple myeloma (MM), also sometimes called Kahler's disease, myelomatosis, or plasma cell myeloma, is cancer that originates in plasma cells. Plasma cells are a type of white blood cell found primarily in bone marrow, which is the soft inner region of bones where blood cells are produced. These cells are part of the body's immune system.
In multiple myeloma, abnormal plasma cells form masses, or tumors, in the bone marrow and bones. Plasma cell myeloma weakens affected bones, reduces numbers of healthy blood cells, increases the risk for infection, and can lead to severe organ damage and other complications. Multiple myeloma is not curable, but often is treatable.
Immune System Anatomy
The immune system is a complex network of tissues and organs that helps the body fight infection and disease. It is made up of special cells (e.g., lymphocytes), tissues (e.g., bone marrow, lymph nodes, lymphatic vessels), and glands and organs (e.g., spleen, thymus, adenoids, tonsils).
Types of lymphocytes include B-cells, T-cells, and null cells (cells without characteristics of T-cells or B-cells). T-cell lymphocytes mature in the thymus gland and are the conductors of the immune system. T-cells initiate the overall immune response and direct B-cells and other cells in this response.
When foreign organisms (e.g., germs, viruses, bacteria) invade the body, B-cell lymphocytes mature into plasma cells. Plasma cells develop in the blood-forming tissues, primarily in the bone marrow. These cells produce proteins called antibodies or immunoglobulins, which are carried throughout the body along with other substances and blood cells (e.g., red blood cells, white blood cells, platelets) in fluid called plasma. Antibodies identify, attack, and destroy the invading organisms (antigens).
Abnormal plasma cells also are called myeloma cells. These cells grow too much and too fast, overproduce specific antibodies (called monoclonal proteins or M proteins), and can lead to formation of a tumor (called a plasmacytoma). In patients who have multiple myeloma, several plasmacytomas develop and high levels of M proteins accumulate throughout the body.
Types of Multiple Myeloma
Multiple myeloma can be classified according to the specific type of M protein that is produced by abnormal plasma cells. The same specific antibody is produced in each patient with multiple myeloma. There are several types of antibodies, including the following:
- Immunoglobulin G (IgG)
- Immunoglobulin A (IgA)
- Immunoglobulin M (IgM)
- Immunoglobulin D (IgD)
- Immunoglobulin E (IgE)
IgG an IgA account for approximately 8090 percent of multiple myeloma cases.
In some cases, myeloma cells produce incomplete M proteins, called Bence Jones proteins (named after Henry Bence Jones, the British physician who discovered them) or light chain proteins. These proteins, which collect primarily in the urine, can cause kidney damage and lead to renal failure. This type of multiple myeloma is called Bence Jones myeloma or light chain myeloma.
Nonsecretory myeloma is a rare form of the disease that accounts for less than 1 percent of all cases. In this type of multiple myeloma, cancerous plasma cells do not produce M proteins.
The earliest form of multiple myeloma is called smoldering myeloma. This type is very-slow growing and usually does not cause symptoms. Patients who have smoldering myeloma undergo frequent testing to monitor progression of the disease.
Incidence and Prevalence of Multiple Myeloma
Overall incidence of multiple myeloma has increased over the past few decades. Multiple myeloma is the second most common cancer of the blood and accounts for about 1 percent of all cancer diagnoses.
According to the World Health Organization (WHO), multiple myeloma and lymphomas (other cancers of the lymphatic system) are the eighth most common type of cancer worldwide, excluding non-melanoma skin cancer. In 2004, approximately 479,000 people were diagnosed with multiple myeloma or lymphoma (e.g., non-Hodgkin’s lymphoma, Hodgkin's disease).
The American Cancer Society reports that about 26,850 cases of multiple myeloma occur each year in the United Statesresulting in about 11,240 deaths. Multiple myeloma is more common in men, in people over the age of 65, and in African Americans.