The epidemiology of multiple myeloma.

Increases in the incidence of multiple myeloma during this past century implicate environmental factors as important causal agents. The molecular and cytogenetic alterations in multiple myeloma are under investigation, but the precise causes of these abnormalities are largely unknown. Exposure to chemical substances and ionizing radiation are associated with an increased risk of multiple myeloma. A single insult is probably not sufficient to induce the disease, which results from the clonal expansion of an idiotypic plasma cell after cumulative mutational damage has altered its genetic makeup. Multiple myeloma does not have the same biology in all patients; it is best viewed as a heterogeneous disease with a different prognosis, clinical course, and response to therapeutic interventions in different subjects. Full details of the genetic background in a given patient are required to better understand the disease. Hopefully this information will be available soon, using DNA array and related technologies.