Three cases of extranodal NK/T-cell lymphoma of the nasal type diagnosed by nasal brush cytology.

Extranodal natural killer (NK)/T-cell lymphoma of the nasal type is a rare type of malignant lymphoma that is most common in Asian countries. Here we describe cytomorphologic, immunocytochemical, and molecular cytochemical features of three cases of NK/T-cell lymphoma of the nasal type diagnosed by nasal brush cytology. Cytomorphologic findings common among the three cases included the presence of several cell types, including nasal cavity epithelial cells, histiocytes, phagocytic histiocytes, and lymphoid cells, within a necrotic background. Suspected lymphoma cells were medium to large lymphoid cells possessing light blue and abundant cytoplasm. A characteristic feature of these cells was the presence of the tongue-like projections of cytoplasm from one or both sides of the cells. We believe these intriguing cytologic findings are indicators of NK/T-cell lymphoma of the nasal type. Azurophilic granules were observed in all cases, ranging from extremely fine granules to large granular lymphocyte (LGL)-like granules. Immunocytochemical and molecular cytochemical analyses showed staining for natural killer cell antigen CD56 as well as cytotoxic granule-associated proteins granzyme B7 (GrB7) and T-cell-restricted intercellular antigen-1 (TIA-1). EBV (Epstein-Barr virus) encoded small RNAs (EBER) positivity was shown by in situ hybridization, and no rearrangement of the TCRgamma gene was observed. Comparison between cytobrush and cotton swab methodology showed that cytobrush resulted in more cell-rich specimens than did cotton swabs, suggesting that nasal brush cytology with cytobrush is most useful in the diagnosis of NK/T-cell lymphoma of the nasal type.