Objective: To determine the incidence of Waldenström macroglobulinemia (WM) in a strictly defined geographic area over a 50-year period. Patients and Methods: All residents of Olmsted County with a diagnosis of WM, consisting of a monoclonal IgM protein of any size and/or 10% or more lymphoplasmacytic infiltration of the bone marrow along with anemia, constitutional symptoms, hyperviscosity, lymphadenopathy, or hepatosplenomegaly requiring therapy, were identified from January 1, 1961, to December 31, 2010. Patients with smoldering WM, lymphoplasmacytic lymphoma with an IgG or IgA monoclonal protein, and those with an IgM monoclonal gammopathy of undetermined significance were excluded. The peripheral blood smears, bone marrow aspirates, and biopsy specimens were reviewed by an experienced hematopathologist. Results: Twenty-two patients were identified as having WM. The age-adjusted incidence rate for males was 0.92 per 100,000 person-years (95% CI, 0.44-1.39 per 100,000 person-years) and for females was 0.30 per 100,000 person-years (95% CI, 0.08-0.53 per 100,000 person-years) with an age- and sex-adjusted incidence of 0.57 per 100,000 person-years (95% CI, 0.33-0.81 per 100,000 person-years). When evaluated using a smoothing spline, there was no convincing evidence for a change in the incidence of WM over the past 50 years. Patients diagnosed with WM after 2000 had an approximately 2-fold excess mortality compared with the expected population mortality (standardized mortality ratio, 2.4; 95% CI, 0.64-6.0). Conclusion: Waldenström macroglobulinemia is a rare malignancy, and the incidence in Olmsted County, Minnesota, has shown virtually no change over the past 50 years.
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