c-Myc Expression Correlates with Plasmablastic Morphology
Sara C Acree, Russell K Brynes, Edward Thornborrow, Imran N Siddiqi. LAC+USC Medical Center, Los Angeles, CA; University of California, San Francisco, CA
Background: Plasmablastic (PB) differentiation can be seen across a spectrum of plasma cell neoplasms. While it is the defining feature in plasmablastic lymphoma, it can occur secondarily in the plasmablastic variant of myeloma, where it portends an aggressive prognosis. MYC gene rearrangement has been well-established in both, thus supporting a biologic link between these entities. Still, the significance of MYC dysregulation in plasma cell neoplasms remains poorly understood, and the association between MYC expression and PB morphology has not been well studied. A recently available c-Myc antibody affords an opportunity to examine associations between MYC expression, plasma cell morphology, and proliferative status.
Design: 63 cases were retrospectively identified. Decalcified specimens were excluded from analysis, limiting our study to extramedullary plasma cell myeloma (PCM, n=24), plasmablastic lymphoma (PBL, n=12), and plasmacytoma (PC, n=27). Each case was assessed for the percentage of tumor cells with PB morphology, previously defined as cells with increased N:C ratio, fine chromatin, large nucleolus, diminished hof region, and decreased cytoplasm (Greipp, 1998). In addition, immunohistochemical (IHC) stains for c-Myc (Epitomics) and Ki-67 were performed, quantified, and compared, respectively, to the PB morphology percentage by linear regression analysis.
Results: PB morphology showed strong correlation (R2=0.92) with c-Myc expression across all plasma cell neoplasms (Figure 1), as well as within each diagnostic category, yielding the following R2 values: PC=0.93, PCM=0.92, and PBL=0.89. In contrast, comparison of PB morphology with Ki-67 had an inferior correlation overall (R2=0.50) and individually: PC=0.75, PCM=0.38, and PBL=0.41.
Conclusions: MYC expression is seen across a spectrum of plasma cell neoplasms, including plasmablastic lymphoma and myeloma, and correlates strongly with PB morphology. As a marker for PB differentiation, MYC IHC has potential diagnostic and prognostic roles in the evaluation of plasma cell neoplasms. The closer association between PB morphology and MYC expression versus proliferation index (Ki-67) supports a role for MYC beyond proliferation in plasma cell neoplasms.
Monday, March 4, 2013 11:45 AM
Proffered Papers: Section C, Monday Morning