Figure 1.

NK-cell gastropathy. The lamina propria is expanded by a dense infiltrate of medium-sized lymphocytes with round nuclei, slightly dispersed chromatin, occasional nucleoli and ample cytoplasm. H&E; original magnification, ×200 (A), ×600 (B). The lymphoid cell population stains negative for both TCRβ (C) and TCRγ (D). They stain positive for CD2 (E), CD3 (F), CD7 (H) but not CD5 (G). Neoplastic lymphocytes may display CD8αα phenotype, being positive for CD8α (I) but not CD8β (J). They display a cytotoxic phenotype with TIA1 expression (K), but in situ hybridization for EBER is negative (L). There is strong expression of CD56 (M), and the proliferation fraction is high at 70% with Ki67 staining (N).