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Figure 1b.  Nasal-type extranodal NK/T-cell lymphoma involving the nasal cavity in a 42-year-old woman. (a) Photomicrograph (original magnification, x400; hematoxylin-eosin [H-E] stain) of a nasal mucosal biopsy specimen shows intense infiltration of atypical lymphoid cells into the vascular intima and subintima (arrow). This is a typical appearance of angiocentric invasion in which the vascular lumen (V) is nearly obstructed. (b) Photomicrograph (original magnification, x200; immunohistochemical stain on paraffin-embedded material) of NK-cell marker (CD56)-labeled tissue shows that atypical lymphoid cells react positively with the marker and appear brown. (c) Photomicrograph (original magnification, x600; in situ hybridization of Epstein-Barr virus on paraffin-embedded material) shows cells labeled with Epstein-Barr virus DNA (arrows).