Incidence of multiple myeloma in Olmsted County, Minnesota

BACKGROUND: Previous studies have indicated that the incidence and mortality rates for multiple myeloma have increased in the United States. The authors reported on the incidence of multiple myeloma in Olmsted County, Minnesota, between 1991 and 2001 and on trends in multiple myeloma incidence over the last 56 years. METHODS: Using the files of the Mayo Clinic and the Olmsted Medical Center (Rochester, MN), the authors identified all residents of Olmsted County who had multiple myeloma, suspected myeloma, or a related disorder. Reports of all laboratory determinations, in addition to autopsy findings and death certificates, were obtained. The criteria for the diagnosis of multiple myeloma have not changed during the last 6 decades. RESULTS: All but 1 of the 47 residents with multiple myeloma first diagnosed between 1991 and 2001 were recognized antemortem. Fifty-five percent had a previous monoclonal gammopathy of undetermined significance, smoldering multiple myeloma, or solitary plasmacytoma before multiple myeloma was diagnosed. From 1991 to 2001, the overall annual incidence rate, age-adjusted to the 2000 U.S. population, was 4.3 per 100,000 (95% confidence interval, 3.0-5.5 per 100,000). Poisson regression analysis showed no statistically significant trend in Olmsted County incidence rates over 56 years. In similar fashion, the authors adjusted multiple myeloma incidence rates from nine other studies worldwide for which adequate data were available and documented similar findings in each case, except for one study that included patients with smoldering multiple myeloma. CONCLUSIONS: The overall incidence of multiple myeloma in Olmsted County, Minnesota, has not changed in almost 6 decades. The apparent increase in incidence elsewhere is unexplained but probably is attributable to improvements in diagnostic techniques, particularly in older patients.