#00010219

Brain biopsy from a 60 year-old patient with a history of solid organ transplant. A predominantly perivascular lymphoid infiltrate with transmural invasion of medium sized blood vessel walls and a concentric growth pattern is seen. The infiltrate consisted mostly of large, transformed cells with large, irregular nuclei, conspicuous nucleoli and increased mitotic activity. By immunohistochemistry, the tumor cells were shown to be variably positive for B-cell markers (CD20, CD79a, PAX5) and BCL6, strongly positive for MUM1 and BCL2, and negative for CD10. The majority of the large cells were positive for EBER by in situ hybridization.