Excerpt from Everyone's Guide to Cancer Therapy. Reproduced with the permission of Malin Dollinger, MD, and Robert A. Kyle, MD.


What we know

Although the exact cause isn't known, doctors do know that multiple myeloma begins with one abnormal plasma cell in your bone marrow — the soft, blood-producing tissue that fills in the center of most of your bones. This abnormal cell then starts to multiply.

Abnormal cells don't mature and then die as normal cells do, they accumulate, eventually overwhelming the production of healthy cells. In healthy bone marrow, less than five percent of the cells are plasma cells. But in people with multiple myeloma, more than ten percent may be plasma cells.

Because myeloma cells may circulate in low numbers in your blood, they can populate bone marrow in other parts of your body, even far from where they began. That's why the disease is called multiple myeloma. Uncontrolled plasma cell growth can damage bones and surrounding tissue. It can also interfere with your immune system's ability to fight infections by inhibiting your body's production of normal antibodies.

Researchers investigating cause

Researchers are studying the DNA of plasma cells to try to understand what changes occur that cause these cells to become cancer cells. Though they haven't yet discovered the cause of these changes, they have found that almost all people with multiple myeloma have genetic abnormalities in their plasma cells that probably contributed to the cancer. For example, many myeloma cells are missing all or part of one chromosome — chromosome 13. Cells with a missing or defective chromosome 13 tend to be more aggressive and harder to treat than are cells with a normal chromosome 13.

A connection with MGUS

Multiple myeloma starts out as a relatively benign condition called monoclonal gammopathy of undetermined significance (MGUS). In the United States, about three percent of people over the age of 50 have MGUS. Each year, about one percent of people with MGUS develop multiple myeloma or a related cancer. This condition, like multiple myeloma, is marked by the presence of M proteins — produced by abnormal plasma cells — in the blood. However, in MGUS, no damage to the body occurs.

Risk factors

Multiple myeloma isn't contagious. Most people who develop multiple myeloma have no clearly identifiable risk factors for the disease. Some factors that may increase your risk of multiple myeloma include:

Age: The majority of people who develop multiple myeloma are older than 50, with most diagnosed in their mid-60s. Few cases occur in people younger than 40.

Sex: Sixty percent of myeloma patients are male.

Race: Blacks are about twice as likely to develop multiple myeloma as are whites. Asians develop the disease least of all.

Obesity: Your risk of multiple myeloma is increased if you're overweight.

Other factors that may increase your risk of developing multiple myeloma include exposure to radiation or pesticides and work in petroleum-related industries.