[1168] IgM Plasma Cell Myeloma: Clinicopathologic Characterization of a Rare Entity

N Cetin, I Bansal, W Bellamy, M Santra, B Barlogie, RB Lorsbach. University of Arkansas for Medical Sciences, Little Rock, AR; Myeloma Institute of Research and Technology, Little Rock, AR

Background: Plasma cell myelomas expressing immunoglobulin (Ig) M are rare, comprising less than 1% of all myeloma. Given their rarity, relatively little is known regarding the clinical and pathologic features of IgM myeloma. In this study, we provide a detailed profile of 18 cases of IgM myeloma, the largest reported series to date.
Design: We retrospectively evaluated the clinical and laboratory data from 18 patients with IgM myeloma between 1998 and 2007. A diagnosis of IgM myeloma was made on the basis of IgM paraproteinemia, infiltration of bone marrow by >10% plasma cells and lack of a morphologically or immunophenotypically detectable B-lymphoid component. Immunohistochemistry (IHC) for CD138, CD56, CD20 and BCL-1(cyclin D1) was performed on the paraffin embedded sections of the bone marrow biopsies (BMB). The morphologic and cytogenetic findings were also reviewed.
Results: The median age at diagnosis was 58 years (range 36-70 years), 67% of patients were male and 78% were Caucasian. The serum IgM protein level at diagnosis was 352-8996 (median 4040) mg/dL in 16/18 cases. Ten and 8 patients had IgM kappa and IgM lambda paraproteins, respectively. Radiologic studies identified lytic bone lesions in 11/16 patients. Random BMB were available in all patients. In each case an interstitial or diffuse infiltrate of plasma cells comprising 10 to >80% was present in 15/18 patients. The remaining 3 patients had either osseous or extramedullary disease (EMD) at diagnosis and no significant plasma cell infiltrate in the random BMB. Three patients developed significant EMD during subsequent stages of their disease. IHC revealed that the myeloma cells in all 18 cases were positive for CD138 and negative for CD56. CD20 was variably positive in 2/16 cases. BCL-1 was expressed in 7/17 cases. Cytogenetics was performed in 17 cases, 5 contained the t(11;14) all of which were positive for BCL-1 by IHC. Five had complex karyotypes lacking the t(11;14), and 7 were normal diploid.
Conclusions: IgM myeloma is a rare entity that is characterized by negativity for CD56 and CD20 in most instances. Most cases are negative for the t(11;14), although this genetic lesion is somewhat overrepresented in IgM myeloma. There is good correlation between BCL-1 detectable by IHC and the presence of the t(11;14) in these cases. While IgM lacks distinctive clinical features, a significant minority of patients with IgM myeloma develop EMD.
Category: Hematopathology

Monday, March 9, 2009 1:45 PM

Platform Session: Section D, Monday Afternoon