Linda M. Pottern, M.P.H., Ph.D.*
|Multiple myeloma is a cancer of the plasma cells that
are usually found in the bone marrow. These cells produce
immunoglobulins or antibodies that normally circulate in the blood
and help ward off disease. The main characteristic of the malignant
plasma cell is the excess production and growth of a specific
immunoglobulin type or a subunit of the immunoglobulin.
Multiple myeloma patients typically seek medical attention because of intermittent bone pain. Characteristic bone lesions seen by X-ray examination accounts for the name "multiple" myeloma and for the earlier classification of this disease as a bone cancer. Other clinical symptoms commonly include anemia, kidney failure, and increased susceptibility to infection.
In 1994, an estimated 12,700 new cases of multiple myeloma were diagnosed in the United States (Boring et al., 1994). Multiple myeloma primarily affects older individuals. In the United States, the median age at onset is 67 for blacks and 71 for whites (Ries et al., 1994). Multiple myeloma is one of the few cancers that occurs twice as frequently in blacks as in whites. The annual incidence for 1987-91 was 11.1 cases per 100,000 for black men and 7.7 for black women, compared with 5.1 for white men and 3.3 for white women (Ries et al., 1994). U.S. blacks experienced the highest incidence of multiple myeloma in the world, while Asians and Hispanics had low rates (Parkin et al., 1992).
The prognosis for multiple myeloma is generally poor. Based on cases diagnosed from 1983 to 1990, U.S. blacks had a slightly higher five-year relative survival rate than whites, 29 percent and 27 percent, respectively (Ries et al., 1994).
Little is known about the etiology of multiple myeloma. Both environmental and genetic factors may play a role in the development of this cancer (Riedel et al., 1992). Exposure to ionizing radiation has been linked with multiple myeloma. The strongest associations have been noted for Japanese atomic bomb survivors (Shimizu, 1990), U.S. radiologists (Matanoski et al., 1975), and radium dial workers (Stebbings et al., 1984). Nuclear power plant workers may also be at an increased risk for developing multiple myeloma (Darby et al., 1988; Gilbert et al., 1989). Living near nuclear facilities, however, does not appear to be associated with myeloma occurrence (Jablon et al., 1990).
Numerous epidemiologic studies have reported a link between multiple myeloma and farming or agricultural work (Riedel et al., 1992). However, it is not clear whether pesticides, agricultural exhausts, chemicals, dusts, or a combination of these exposures are the responsible agents. Other nonspecific occupational exposures that have been associated with myeloma include metals, rubber, wood, leather, paint, and petroleum (Riedel et al., 1992). Workplace exposure to benzene, a chemical used in many manufacturing processes, may play a role in the development of multiple myeloma (Decoufle et al., 1983; Rinsky et al., 1987).
It has been a longstanding belief that prolonged stimulation of the immune system by repeated infections, allergic conditions, or autoimmune disease may increase the risk of myeloma. The current scientific evidence is weak. A few studies have reported elevated myeloma risks with specific medical conditions such as allergies, rheumatoid arthritis, and rheumatic fever, while other studies have not found these or other such associations (Riedel et al., 1992).
The occurrence of multiple myeloma among siblings, spouses, and family members of myeloma patients suggests that genetic factors and common environmental exposures play a role in the development of this cancer (Riedel et al., 1992). The discovery of specific human leukocyte antigens (HLA) (Leech, 1983; Pottern et al., 1992), chromosome abnormalities (Lewis and MacKenzie, 1984; Nishida et al., 1989) and oncogenes (Ernst et al., 1988; Gould et al., 1988; Selvanayagam et al., 1988) among myeloma patients adds further support for a genetic predisposition for this cancer.
A link between cigarette smoking and myeloma has been suggested in a recent study (Mills et al., 1990); however, this association has not been shown in other studies (Gallagher et al., 1983; Flodin et al., 1987; Linet et al., 1987; Brown et al., 1992; Heineman et al., 1992). Other lifestyle factors, such as dietary patterns and alcohol consumption, have yet to be fully explored in epidemiologic investigations of multiple myeloma.