AbstractWe have compared histologic features and gene expression profiles of newly identified plasmacytomas from NFS.V+ congenic mice with plasmacytomas of IL6 transgenic, Fasl mutant, and SJL-β2M−/− mice. NFS.V+ tumors comprised an overlapping morphologic spectrum of high-grade/anaplastic, intermediate-grade/plasmablastic, and low-grade/plasmacytic cases with similarities to subsets of human multiple myeloma and plasmacytoma. Microarray and immunohistochemical analyses of genes expressed by the most prevalent tumors, plasmablastic plasmacytomas, showed them to be most closely related to immunoblastic lymphomas, less so to plasmacytomas of Fasl mutant and SJL mice, and least to plasmacytic plasmacytomas of IL6 transgenic mice. Plasmablastic tumors seemed to develop in an inflammatory environment associated with gene signatures of T cells, natural killer cells, and macrophages not seen with plasmacytic plasmacytomas. Plasmablastic plasmacytomas from NFS.V+ and SJL-β2M−/− mice did not have structural alterations in Myc or T(12;15) translocations and did not express Myc at high levels, regular features of transgenic and pristane-induced plasmacytomas. These findings imply that, as for human multiple myeloma, Myc-independent routes of transformation contribute to the pathogenesis of these tumors. These findings suggest that plasma cell neoplasms of mice and humans exhibit similar degrees of complexity. Mouse plasmacytomas, previously considered to be homogeneous, may thus be as diverse as their human counterparts with respect to oncogenic mechanisms of plasma cell transformation. Selecting specific types of mouse plasmacytomas that relate most closely to subtypes of human multiple myeloma may provide new opportunities for preclinical testing of drugs for treatment of the human disease. [Cancer Res 2007;67(6):2439–47]