A stereotactic biopsy was performed under general anesthesia on the 98th day after admission. The tissue sections of the biopsy specimens were prepared for hematoxylin-eosin (HE) staining, periodic acid-Schiff staining, immunohistochemistry for antibodies (glial fibrillary acidic protein, cluster of differentiation 3 (CD3), CD4, CD8, CD10, CD20, CD68, CD79a, T-cell intracytoplasmic antigen-1 (TIA-1), granzyme B, latent membrane protein (LMP), Epstein-Barr virus nuclear antigen 2 (EBNA2), and Ki-67), and in situ hybridization for Epstein-Barr virus expressing mRNA (EBER). Cells in the tissue were extracted, and surface markers were analyzed by flow cytometry. The karyotype was assessed by G-banding.