MICROSCOPIC DESCRIPTION: Nerve root infiltrated by a neoplastic lymphoid infiltrate. The tumour cells are large, with fairly small amounts of cytoplasm and large irregular nuclei, often with prominent nucleoli. The neoplastic cells show strong membrane enhanced cytoplasmic staining with the antibody to CD20. There is an accompanying infiltrate of small lymphocytes, of both B and T-cell lineage. The features are those of infiltration of nerve root by diffuse large B-cell non-Hodgkin lymphoma.