Swedish scientists have identified agricultural and baking occupations, among others, as having excess risk for multiple myeloma, which they attributed to high exposure of chemicals and sensitizing agents. Although several risk factors (including male gender, age, and African-American ethnicity) had been previously established, no environmental risk factors had been identified.

Nearly three million Swedish workers were categorized by occupation and age, and their health records were tracked between 1971 and 1989. Scientists tracked these records through the National Cancer and Death Registries to determine if workers had been diagnosed with multiple myeloma.

At the conclusion of the nineteen-year study, 3,127 men and 1,282 women had been diagnosed with multiple myeloma. The results indicated an excess risk of multiple myeloma for bakers and pastry cooks. Other occupations were assessed to have an elevated risk of multiple myeloma. For men, these included agricultural, horticultural, and forestry workers; dental technicians; stonecutters and carvers; and prison and reformatory officials. For women, these included psychiatric care attendants, metal workers, and paper workers.

Scientists classified each occupation by its exposure to thirteen chemicals. The categories included “unexposed” (less than 10 percent of workers exposed to high chemical levels), “possible exposure” (10 to 66 percent of workers exposed to such levels), and “probable exposure” (more than 66 percent of workers exposed to such levels). The study assessed exposure to asbestos, chromium, nickel, lead, mercury, metals, oil mist, polycyclic aromatic hydrocarbons, pesticides, herbicides, pesticide and herbicide sprayers, petroleum products, quartz, solvents, and textile dust.

Exposure to high and low molecular weight sensitizing agents was also assessed. Scientists classified each occupation by its exposure in the same method as described for chemicals. High molecular weight agents include allergenic proteins, and low molecular weight agents include a variety of highly reactive chemicals, antigenic wood dusts, and metal antigens.

Occupational assessment of exposure to chemicals and sensitizing agents indicated that women were less exposed than men. The only significant excess risk was associated with the use of pesticides and herbicides by men in the agricultural, horticultural, and forestry enterprises. Some herbicides are capable of impairing cytokine production and inducing immunosuppression, two possible mechanisms leading to multiple myeloma.

Bakers and pastry cooks had the most significant excess risk for exposure to high molecular weight agents, which typically included certain fungal enzymes and flour dust. These allergens cause respiratory problems, and one possible explanation is that chronic immune stimulation promotes multiple myeloma.

The researchers report their findings in the November 1, 2008 issue of Cancer Epidemiology Biomarkers & Prevention.