Multiple myeloma is a blood cancer that develops from abnormal plasma cells in the bone marrow. In healthy patients, plasma cells, which are a normal type of white blood cell of the immune system, produce antibodies to help fight infection. In myeloma, plasma cells transform into cancerous cells and produce increased amounts of antibodies (immunoglobulins) called monoclonal proteins (M-spike), as well as incomplete antibodies (light chains or Bence-Jones proteins). The myeloma cells take over the bone marrow and prevent the production of normal blood cells, and the abnormal proteins produced by myeloma cells can cause organ damage, especially in the kidneys. Cancerous myeloma cells may lead to soft spots in the bone, called osteolytic lesions, which weaken the bones and result in an increased risk of fractures. The main types of organ damage caused by multiple myeloma are described by the acronym CRAB: C, calcium elevation; R, renal (kidney) dysfunction; A, anemia; B, bone disease.
Definitions of MGUS, Myeloma, Plasmacytoma, Amyloidosis
- Monoclonal Gammopathy of Undetermined Significance (MGUS): Precursor to myeloma. Patients with MGUS do not have cancer, but are monitored for signs of progression to myeloma. Patients usually have an M-spike, but no CRAB features. Most patients with active myeloma initially had MGUS.
- Smoldering myeloma: Asymptomatic disease. Patients are usually only monitored and may be treated with bone-strengthening medicines called bisphosphonates. Ongoing research will help us determine if treatment with myeloma drugs will benefit patients with smoldering disease.
- Active myeloma: Symptomatic disease. Patients with active myeloma require immediate evaluation by a myeloma specialist to come up with a personalized treatment plan.
- Solitary plasmacytoma: An abnormal plasma cell growth occurring in only one location. Solitary plasmacytomas are most often treated with radiation, and sometimes with surgery. Patients are monitored closely because there is a risk of later developing multiple myeloma.
- Amyloidosis: Abnormal protein deposition in tissues. In amyloidosis, also called AL or primary amyloidosis, abnormal plasma cells make too many light chains (a protein component of antibodies). The abnormal light chains can accumulate and deposit in tissues and organs, especially in the heart and kidneys, causing organ dysfunction.
Multiple myeloma is the second most common blood cancer diagnosed in the United States, after non-Hodgkin lymphoma. It represents approximately 1 percent of all cancers. The American Cancer Society estimates that 30,280 new cases of multiple myeloma will be diagnosed in the United States in 2017, and an estimated 103,463 Americans are living with or in remission from myeloma.
Causes and risk factors
The cause of myeloma is still unknown. Scientists have discovered that mutations in certain oncogenes — genes that promote cells to grow and divide — occur in various stages of multiple myeloma. These oncogenes include MYC, RAS, and p53. Abnormalities in chromosomes (how DNA is packaged in the cell), including translocations, deletions, and duplications, are also important for the development and progression of multiple myeloma.
We do know that myeloma occurs more frequently with increasing age, is more common among men than women, and is twice as common among African Americans as among Caucasians.
Research suggests several possible risk factors for the disease, including:
- A decline in the immune system
- Having other plasma cell diseases such as monoclonal gammopathy of undetermined significance (MGUS).
- Exposure to radiation.
- Exposure to certain chemicals, including benzene, Agent Orange, and agricultural chemicals.
- Infection with cancer-causing viruses, including HIV, hepatitis viruses, and several herpes viruses.
It is uncommon for myeloma to affect more than one member of a family.
Because an exact cause is unknown, there is no known way to prevent myeloma.