Sections demonstrate a extensive ulceration at low power with subjacent areas showing a diffuse lymphoid infiltrate (on the left in the image) with large/plasmablastic cytomorphology (at higher power). Scattered histiocytes are noted imparing a "starry-sky" appearance often seen in highly proliferative processes including Burkitt lymphoma.

CD20 (image on left) and CD79a (image on right) are both negative in this case. Lack of CD20 is consistent with a plasmablastic phenotype. Although most PBL often express CD79a which plasmacytic cells retain, this case is negative. Rare scattered background small B-cell or plasma cell staining for CD20 or CD79a respectively are noted in these stains.

CD45, a marker often used to identify hematopoietic lineage is typically negative in plasmablastic lymphoma. Certain hematopoietic proliferations often lack CD45 and these include Hodgkin lymphoma, anaplastic large cell lymphoma and lymphoblastic processes. Hence, the lack of CD45 in an undifferentiated neoplasm should not automatically rule out a hematopoietic process. The image shows background CD45 lymphocytes while the lymphoma cells are negative in this case.

Both CD138 (left image, membranous pattern) and MUM1 (right image nuclear stain), markers of a plasmacytic phenotype are positive on the lymphoma cells.

EBV by in situ hybridization is positive in the lymphoma cells (nuclear pattern).

Programmed death receptor ligand-1 (PD-L1) stains the background histiocytes in a membranous fashion but the adjoining lymphoma cells are negative for this stain.