Immunohistochemical analysis and EBER ISH in a case with NK-cell phenotype (case 15). (A) Hematoxylin and eosin (H&E) stain of a skin biopsy with a dense infiltrate extending from the upper dermis deep into the subcutaneous tissue (original magnification ×12.5). (B-E) Higher magnification shows atypical lymphoid cells with rimming of individual fat cells mimicking subcutaneous panniculitis-like T-cell lymphoma (B). The cells are EBER positive (C), strongly and homogeneously CD56 positive (D), and TIA-1 positive (E). (B-E: original magnification ×400). (F) Higher magnification of the dermis reveals angioinvasion with abundant eosinophils (original magnification ×400). (G) CD30 stain shows many positive cells. (H) LMP1 is positive only in a few scattered cells (G-H: immunohistochemistry, original magnification ×400). (I-K) Comparative morphology of 3 skin biopsies in case 15. (I) Skin biopsy at diagnosis shows a lymphoid infiltrate of rather small lymphocytes without atypia. (J) Skin biopsy 1 year after diagnosis shows a lymphoid infiltrate composed of medium-sized cells with abundant clear cytoplasm. (K) Skin biopsy 7 years after the original diagnosis with rather atypical large cells, abundant clear cytoplasm, and prominent nucleoli (I-K: H&E stain, original magnification ×400).