Gene-targeted iMycEμ mice that carry a His6-tagged mouse Myc(c-myc)cDNA, MycHis, just 5' of the immunoglobulin heavy-chain enhancer, Eμ, are prone to B cell and plasma cell neoplasms, such as lymphoblastic B-cell lymphoma (LBL) and plasmacytoma (PCT). The gene discussed is MYC; the disease is plasmacytoma.