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What Is Multiple Myeloma - Causes and Incidence

Causes and Incidence

Multiple myeloma is the second most prevalent blood cancer after non-Hodgkin's lymphoma. It represents approximately 1% of all cancers in white US residents and 2% of cancers in black residents.

Recent statistics indicate both increasing incidence and earlier age of onset. The average age at diagnosis is 69 years for men and 71 years for women, and only 4% of cases are diagnosed in individuals under the age of 45. Approximately 66,000 Americans had myeloma in 2009 (the most current date these statistics are available) and the American Cancer Society estimates that approximately 20,580 new cases of myeloma will be diagnosed during 2009.

Multiple myeloma occurs more frequently in men than women (of the estimated 20,580 new cases referenced above, 11,680 are expected to occur in men versus 8,900 in women). African Americans have the highest reported incidence of this disease and Asians the lowest. Among African Americans, myeloma is one of the leading causes of cancer death.

Although a tremendous amount of work has gone into the search for the cause of multiple myeloma, to date no cause for this disease has been identified. However, the search for a cause has suggested possible associations between myeloma and a decline in the immune system, genetic factors, certain occupations, certain viruses, exposure to certain chemicals including Agent Orange, and exposure to radiation.

Age is the most significant risk factor for multiple myeloma, as 96% of cases are diagnosed in people over the age of 45, and more than 60% occur in people over the age of 65. Because the peak age for multiple myeloma is among the elderly it is thought that susceptibility may increase with the aging process and the consequent reduction in immune surveillance of evolving cancer, or that myeloma may result from a lifelong accumulation of toxic insults or antigenic challenges.

The higher incidence of myeloma in African Americans and the much less frequent occurrence in Asians suggest genetic factors. While it is uncommon for myeloma to develop in more than one family member, there is a slight increased risk among children and siblings of those with myeloma.

People in agricultural occupations, petroleum workers, workers in leather industries, and cosmetologists all seem to have a higher-than-average chance of developing multiple myeloma. Exposure to herbicides, insecticides, petroleum products, heavy metals, plastics, and various dusts including asbestos also appear to be risk factors for the disease. In addition, individuals exposed to large amounts of radiation, such as survivors of the atomic bomb explosions in Japan, have an increased risk for myeloma, although this accounts for a very small number of cases.

Chromosomal changes including chromosomal translocations (generally involving the Ig heavy chain gene), and chromosomal gains and losses are very frequent in myeloma. These abnormalities have an important influence on disease outcome.

It is important to remember that in most cases, individuals who develop multiple myeloma have no clear risk factors. Myeloma may be the result of several factors acting together.