Plasmablastic lymphoma is a high grade B cell lymphoma with plasmablastic morphology and a terminally differentiated B cell immunophenotype, usually arising in the setting of immunodeficiency and often demonstrating Epstein Barr Virus positivity. The molecular and genetic mechanisms underlying the pathogenesis of PBL are largely unknown. To better understand its pathogenesis, herein we have analyzed global gene expression of PBL and compared that to gene expression profiles of diffuse large B cell lymphoma. While overlaps in transcriptomes between these malignancies were identified, we have shown that the gene expression profile of plasmablastic lymphoma is distinct, demonstrating striking downregulation of B cell receptor signaling genes, BCL6, BCL11A SPI-B, targets of NFKB1, and upregulation of mitochondrial genes, PRMT5, MYC and MYC targets and IL21, implicating these alterations in the pathogenesis of this lymphoma. In addition we show the usefulness of SWAP-70 immunohistochemistry in the differentiation of immunoblastic diffuse large B cell lymphoma and plasmablastic lymphoma. Our findings provide justification for considering plasmablastic lymphoma as a specific lymphoma entity and provide insight into the unique transcriptional aberrations occurring in this high-grade lymphoma.